Merge branch 'master' of https://github.com/MoonchildProductions/UXP

25 files changed, 3400 insertions, 1020 deletions

diff --git a/application/basilisk/branding/official/branding.nsi b/application/basilisk/branding/official/branding.nsi
index 58d7554df..250abd84d 100644
--- a/application/basilisk/branding/official/branding.nsi
+++ b/application/basilisk/branding/official/branding.nsi
@@ -12,39 +12,5 @@
 !define CompanyName           "Moonchild Productions"
 !define URLInfoAbout          "https://www.basilisk-browser.org"
 !define URLUpdateInfo         "https://www.basilisk-browser.org/releasenotes.shtml"
-!define HelpLink              "https://www.basilisk-browser.org"
-
-; The OFFICIAL define is a workaround to support different urls for Release and
-; Beta since they share the same branding when building with other branches that
-; set the update channel to beta.
-!define OFFICIAL
-!define URLStubDownload ""
-!define URLManualDownload ""
-!define URLSystemRequirements "http://www.basilisk-browser.org/requirements.shtml"
-!define Channel "release"
-
-# The installer's certificate name and issuer expected by the stub installer
-!define CertNameDownload   ""
-!define CertIssuerDownload ""
-
-# Dialog units are used so the UI displays correctly with the system's DPI
-# settings.
-# The dialog units for the bitmap's dimensions should match exactly with the
-# bitmap's width and height in pixels.
-!define APPNAME_BMP_WIDTH_DU "134u"
-!define APPNAME_BMP_HEIGHT_DU "36u"
-!define INTRO_BLURB_WIDTH_DU "258u"
-!define INTRO_BLURB_EDGE_DU "170u"
-!define INTRO_BLURB_LTR_TOP_DU "20u"
-!define INTRO_BLURB_RTL_TOP_DU "12u"
-
-# UI Colors that can be customized for each channel
-!define FOOTER_CONTROL_TEXT_COLOR_NORMAL 0x000000
-!define FOOTER_CONTROL_TEXT_COLOR_FADED 0x666666
-!define FOOTER_BKGRD_COLOR 0xFFFFFF
-!define INTRO_BLURB_TEXT_COLOR 0x666666
-!define INSTALL_BLURB_TEXT_COLOR 0x666666
-!define INSTALL_PROGRESS_TEXT_COLOR_NORMAL 0x666666
-!define COMMON_TEXT_COLOR_NORMAL 0x000000
-!define COMMON_TEXT_COLOR_FADED 0x666666
-!define COMMON_BKGRD_COLOR 0xF0F0F0
+!define HelpLink              "https://www.basilisk-browser.org/contact.shtml"
+!define URLSystemRequirements "https://www.basilisk-browser.org/requirements.shtml"
diff --git a/application/basilisk/branding/unofficial/branding.nsi b/application/basilisk/branding/unofficial/branding.nsi
index 77f08a4cb..586dd0074 100644
--- a/application/basilisk/branding/unofficial/branding.nsi
+++ b/application/basilisk/branding/unofficial/branding.nsi
@@ -10,36 +10,7 @@
 # instead of BrandFullName and typically should not be modified.
 !define BrandFullNameInternal "Serpent"
 !define CompanyName           "Moonchild Productions"
-!define URLInfoAbout          "http://www.basilisk-browser.org"
+!define URLInfoAbout          "https://www.basilisk-browser.org"
+!define URLUpdateInfo         "https://www.basilisk-browser.org"
 !define HelpLink              "https://forum.palemoon.org"
-
-!define URLStubDownload ""
-!define URLManualDownload ""
-!define URLSystemRequirements ""
-!define Channel "unofficial"
-
-# The installer's certificate name and issuer expected by the stub installer
-!define CertNameDownload   ""
-!define CertIssuerDownload ""
-
-# Dialog units are used so the UI displays correctly with the system's DPI
-# settings.
-# The dialog units for the bitmap's dimensions should match exactly with the
-# bitmap's width and height in pixels.
-!define APPNAME_BMP_WIDTH_DU 159u
-!define APPNAME_BMP_HEIGHT_DU 50u
-!define INTRO_BLURB_WIDTH_DU "230u"
-!define INTRO_BLURB_EDGE_DU "198u"
-!define INTRO_BLURB_LTR_TOP_DU "16u"
-!define INTRO_BLURB_RTL_TOP_DU "11u"
-
-# UI Colors that can be customized for each channel
-!define FOOTER_CONTROL_TEXT_COLOR_NORMAL 0x000000
-!define FOOTER_CONTROL_TEXT_COLOR_FADED 0x999999
-!define FOOTER_BKGRD_COLOR 0xFFFFFF
-!define INTRO_BLURB_TEXT_COLOR 0xFFFFFF
-!define INSTALL_BLURB_TEXT_COLOR 0xFFFFFF
-!define INSTALL_PROGRESS_TEXT_COLOR_NORMAL 0xFFFFFF
-!define COMMON_TEXT_COLOR_NORMAL 0xFFFFFF
-!define COMMON_TEXT_COLOR_FADED 0xA1AAB3
-!define COMMON_BKGRD_COLOR 0x0F1B26
+!define URLSystemRequirements "https://www.basilisk-browser.org"
diff --git a/application/basilisk/installer/windows/Makefile.in b/application/basilisk/installer/windows/Makefile.in
index d5580b53d..bab6ded1a 100644
--- a/application/basilisk/installer/windows/Makefile.in
+++ b/application/basilisk/installer/windows/Makefile.in
@@ -79,10 +79,6 @@ $(CONFIG_DIR)/setup.exe::
 	$(PYTHON) $(topsrcdir)/toolkit/mozapps/installer/windows/nsis/preprocess-locale.py \
 	  --preprocess-locale $(topsrcdir) \
 	  $(PPL_LOCALE_ARGS) $(AB_CD) $(CONFIG_DIR)
-	$(PYTHON) $(topsrcdir)/toolkit/mozapps/installer/windows/nsis/preprocess-locale.py \
-	  --preprocess-single-file $(topsrcdir) \
-	  $(PPL_LOCALE_ARGS) $(CONFIG_DIR) \
-	  nsisstrings.properties nsisstrings.nlf
 
 GARBARGE_DIRS += instgen
 
diff --git a/application/basilisk/installer/windows/nsis/defines.nsi.in b/application/basilisk/installer/windows/nsis/defines.nsi.in
index 5ad9b7966..dbb58ca33 100644
--- a/application/basilisk/installer/windows/nsis/defines.nsi.in
+++ b/application/basilisk/installer/windows/nsis/defines.nsi.in
@@ -3,23 +3,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-# Defining FunnelcakeVersion will append the value of StubURLVersionAppend to
-# StubURLVersion, append the value of URLManualDownloadAppend to
-# URLManualDownload, and append the value of URLStubDownloadAppend to
-# URLStubDownload. The value of FunnelcakeVersion should not be defined when it
-# is not used and when it is defined its value should never be empty.
-# !define FunnelcakeVersion        "999"
-
-!ifdef FunnelcakeVersion
-!define URLManualDownloadAppend  "&f=${FunnelcakeVersion}"
-!define URLStubDownloadAppend    "-f${FunnelcakeVersion}"
-!define StubURLVersionAppend     "-${FunnelcakeVersion}"
-!else
-!define URLManualDownloadAppend  ""
-!define URLStubDownloadAppend    ""
-!define StubURLVersionAppend     ""
-!endif
-
 # These defines should match application.ini settings
 !define AppName               "Basilisk"
 !define AppVersion            "@APP_VERSION@"
@@ -84,13 +67,3 @@ VIAddVersionKey "FileVersion"     "${AppVersion}"
 VIAddVersionKey "ProductVersion"  "${AppVersion}"
 # Comments is not used but left below commented out for future reference
 # VIAddVersionKey "Comments"        "Comments"
-
-# Control positions in Dialog Units so they are placed correctly with
-# non-default DPI settings
-!define OPTIONS_ITEM_EDGE_DU 90u
-!define OPTIONS_ITEM_WIDTH_DU 356u
-!define OPTIONS_SUBITEM_EDGE_DU 119u
-!define OPTIONS_SUBITEM_WIDTH_DU 327u
-!define INSTALL_BLURB_TOP_DU 78u
-!define APPNAME_BMP_EDGE_DU 19u
-!define APPNAME_BMP_TOP_DU 12u
diff --git a/application/basilisk/locales/en-US/installer/nsisstrings.properties b/application/basilisk/locales/en-US/installer/nsisstrings.properties
deleted file mode 100644
index 389405696..000000000
--- a/application/basilisk/locales/en-US/installer/nsisstrings.properties
+++ /dev/null
@@ -1,67 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-# LOCALIZATION NOTE:
-
-# This file must be saved as UTF8
-
-# Accesskeys are defined by prefixing the letter that is to be used for the
-# accesskey with an ampersand (e.g. &).
-
-# Do not replace $BrandShortName, $BrandFullName, or $BrandFullNameDA with a
-# custom string and always use the same one as used by the en-US files.
-# $BrandFullNameDA allows the string to contain an ampersand (e.g. DA stands
-# for double ampersand) and prevents the letter following the ampersand from
-# being used as an accesskey.
-
-# You can use \n to create a newline in the string but only when the string
-# from en-US contains a \n.
-
-WIN_CAPTION=$BrandShortName Setup
-
-INTRO_BLURB1=Thanks for choosing $BrandFullName, the browser that chooses you above everything else.
-INSTALL_BLURB1=You're about to enjoy the very latest in speed, flexibility and security so you're always in control.
-INSTALL_BLURB2=That's because $BrandShortName is made by a non-profit to make browsing and the Web better for you.
-INSTALL_BLURB3=You're also joining a global community of users, contributors and developers working to make the best browser in the world.
-
-WARN_MIN_SUPPORTED_OSVER_MSG=Sorry, $BrandShortName can't be installed. This version of $BrandShortName requires ${MinSupportedVer} or newer. Please click the OK button for additional information.
-WARN_MIN_SUPPORTED_CPU_MSG=Sorry, $BrandShortName can't be installed. This version of $BrandShortName requires a processor with ${MinSupportedCPU} support. Please click the OK button for additional information.
-WARN_MIN_SUPPORTED_OSVER_CPU_MSG=Sorry, $BrandShortName can't be installed. This version of $BrandShortName requires ${MinSupportedVer} or newer and a processor with ${MinSupportedCPU} support. Please click the OK button for additional information.
-WARN_WRITE_ACCESS=You don't have access to write to the installation directory.\n\nClick OK to select a different directory.
-WARN_DISK_SPACE=You don't have sufficient disk space to install to this location.\n\nClick OK to select a different location.
-WARN_ROOT_INSTALL=Unable to install to the root of your disk.\n\nClick OK to select a different location.
-WARN_MANUALLY_CLOSE_APP_LAUNCH=$BrandShortName is already running.\n\nPlease close $BrandShortName prior to launching the version you have just installed.
-
-ERROR_DOWNLOAD=Your download was interrupted.\n\nPlease click the OK button to continue.
-
-INSTALL_BUTTON=&Install
-UPGRADE_BUTTON=&Upgrade
-CANCEL_BUTTON=Cancel
-OPTIONS_BUTTON=&Options
-
-MAKE_DEFAULT=&Make $BrandShortName my default browser
-CREATE_SHORTCUTS=Create Shortcuts for $BrandShortName:
-ADD_SC_TASKBAR=On my &Task bar
-ADD_SC_QUICKLAUNCHBAR=On my &Quick Launch bar
-ADD_CheckboxShortcutInStartMenu=In my &Start Menu Programs Folder
-ADD_CheckboxShortcutOnDesktop=On my &Desktop
-SPACE_REQUIRED=Space Required:
-SPACE_AVAILABLE=Space Available:
-ONE_MOMENT_INSTALL=One moment, $BrandShortName will launch as soon as the install is complete…
-ONE_MOMENT_UPGRADE=One moment, $BrandShortName will launch as soon as the upgrade is complete…
-INSTALL_MAINT_SERVICE=&Install the $BrandShortName background update service
-SEND_PING=S&end information about this installation to Mozilla
-BROWSE_BUTTON=B&rowse…
-DEST_FOLDER=Destination Folder
-
-DOWNLOADING_LABEL=Downloading $BrandShortName…
-INSTALLING_LABEL=Installing $BrandShortName…
-UPGRADING_LABEL=Upgrading $BrandShortName…
-
-SELECT_FOLDER_TEXT=Select the folder to install $BrandShortName in.
-
-BYTE=B
-KILO=K
-MEGA=M
-GIGA=G
diff --git a/application/palemoon/branding/official/branding.nsi b/application/palemoon/branding/official/branding.nsi
index 2b6dbe7bd..3bceda900 100644
--- a/application/palemoon/branding/official/branding.nsi
+++ b/application/palemoon/branding/official/branding.nsi
@@ -11,39 +11,6 @@
 !define BrandFullNameInternal "Pale Moon"
 !define CompanyName           "Moonchild Productions"
 !define URLInfoAbout          "http://www.palemoon.org/"
-!define URLUpdateInfo         "http://www.palemoon.org/releasenotes-ng.shtml"
-
-; The OFFICIAL define is a workaround to support different urls for Release and
-; Beta since they share the same branding when building with other branches that
-; set the update channel to beta.
-!define OFFICIAL
-!define URLStubDownload ""
-!define URLManualDownload "http://www.palemoon.org/download-ng.shtml"
-!define Channel "release"
-
-# The installer's certificate name and issuer expected by the stub installer
-# !define CertNameDownload   "Mozilla Corporation"
-# !define CertIssuerDownload "Thawte Code Signing CA - G2"
-
-# Dialog units are used so the UI displays correctly with the system's DPI
-# settings.
-# The dialog units for the bitmap's dimensions should match exactly with the
-# bitmap's width and height in pixels.
-!define APPNAME_BMP_WIDTH_DU "134u"
-!define APPNAME_BMP_HEIGHT_DU "36u"
-!define INTRO_BLURB_WIDTH_DU "258u"
-!define INTRO_BLURB_EDGE_DU "170u"
-!define INTRO_BLURB_LTR_TOP_DU "20u"
-!define INTRO_BLURB_RTL_TOP_DU "12u"
-
-# UI Colors that can be customized for each channel
-!define FOOTER_CONTROL_TEXT_COLOR_NORMAL 0x000033
-!define FOOTER_CONTROL_TEXT_COLOR_FADED 0x666699
-!define FOOTER_BKGRD_COLOR 0xFFFFFF
-!define INTRO_BLURB_TEXT_COLOR 0x666699
-!define OPTIONS_TEXT_COLOR_NORMAL 0x000000
-!define OPTIONS_TEXT_COLOR_FADED 0x666699
-!define OPTIONS_BKGRD_COLOR 0xF0F0F0
-!define INSTALL_BLURB_TEXT_COLOR 0x666699
-!define INSTALL_PROGRESS_TEXT_COLOR_NORMAL 0x666699
-!define INSTALL_PROGRESS_TEXT_COLOR_FADED 0x9999C0
+!define URLUpdateInfo         "http://www.palemoon.org/releasenotes.shtml"
+!define HelpLink              "http://www.palemoon.org/troubleshooting.shtml"
+!define URLSystemRequirements "http://www.palemoon.org/download.shtml"
diff --git a/application/palemoon/branding/unofficial/branding.nsi b/application/palemoon/branding/unofficial/branding.nsi
index cf1642eaf..62ed242a2 100644
--- a/application/palemoon/branding/unofficial/branding.nsi
+++ b/application/palemoon/branding/unofficial/branding.nsi
@@ -12,29 +12,5 @@
 !define CompanyName           "Moonchild Productions"
 !define URLInfoAbout          "http://www.palemoon.org"
 !define URLUpdateInfo         "http://www.palemoon.org"
-
-!define URLManualDownload "http://www.palemoon.org/download-ng.shtml"
-!define Channel "unofficial"
-
-# Dialog units are used so the UI displays correctly with the system's DPI
-# settings.
-# The dialog units for the bitmap's dimensions should match exactly with the
-# bitmap's width and height in pixels.
-!define APPNAME_BMP_WIDTH_DU 159u
-!define APPNAME_BMP_HEIGHT_DU 26u
-!define INTRO_BLURB_WIDTH_DU "230u"
-!define INTRO_BLURB_EDGE_DU "198u"
-!define INTRO_BLURB_LTR_TOP_DU "16u"
-!define INTRO_BLURB_RTL_TOP_DU "11u"
-
-# UI Colors that can be customized for each channel
-!define FOOTER_CONTROL_TEXT_COLOR_NORMAL 0x000000
-!define FOOTER_CONTROL_TEXT_COLOR_FADED 0x999999
-!define FOOTER_BKGRD_COLOR 0xFFFFFF
-!define INTRO_BLURB_TEXT_COLOR 0xFFFFFF
-!define OPTIONS_TEXT_COLOR_NORMAL 0xFFFFFF
-!define OPTIONS_TEXT_COLOR_FADED 0xA1AAB3
-!define OPTIONS_BKGRD_COLOR 0x0F1B26
-!define INSTALL_BLURB_TEXT_COLOR 0xFFFFFF
-!define INSTALL_PROGRESS_TEXT_COLOR_NORMAL 0xFFFFFF
-!define INSTALL_PROGRESS_TEXT_COLOR_FADED 0xA1AAB3
+!define HelpLink              "http://www.palemoon.org"
+!define URLSystemRequirements "http://www.palemoon.org/download.shtml"
diff --git a/application/palemoon/branding/unstable/branding.nsi b/application/palemoon/branding/unstable/branding.nsi
index 4a9199b22..535cfde33 100644
--- a/application/palemoon/branding/unstable/branding.nsi
+++ b/application/palemoon/branding/unstable/branding.nsi
@@ -11,36 +11,6 @@
 !define BrandFullNameInternal "Pale Moon"
 !define CompanyName           "Moonchild Productions"
 !define URLInfoAbout          "http://www.palemoon.org/"
-!define URLUpdateInfo         "http://www.palemoon.org/unstable.shtml"
-
-; The OFFICIAL define is a workaround to support different urls for Release and
-; Beta since they share the same branding when building with other branches that
-; set the update channel to beta.
-!define OFFICIAL
-!define URLStubDownload ""
-!define URLManualDownload "http://www.palemoon.org/unstable.shtml"
-!define Channel "unstable"
-
-
-# Dialog units are used so the UI displays correctly with the system's DPI
-# settings.
-# The dialog units for the bitmap's dimensions should match exactly with the
-# bitmap's width and height in pixels.
-!define APPNAME_BMP_WIDTH_DU "134u"
-!define APPNAME_BMP_HEIGHT_DU "36u"
-!define INTRO_BLURB_WIDTH_DU "258u"
-!define INTRO_BLURB_EDGE_DU "170u"
-!define INTRO_BLURB_LTR_TOP_DU "20u"
-!define INTRO_BLURB_RTL_TOP_DU "12u"
-
-# UI Colors that can be customized for each channel
-!define FOOTER_CONTROL_TEXT_COLOR_NORMAL 0x000033
-!define FOOTER_CONTROL_TEXT_COLOR_FADED 0x666699
-!define FOOTER_BKGRD_COLOR 0xFFFFFF
-!define INTRO_BLURB_TEXT_COLOR 0x666699
-!define OPTIONS_TEXT_COLOR_NORMAL 0x000000
-!define OPTIONS_TEXT_COLOR_FADED 0x666699
-!define OPTIONS_BKGRD_COLOR 0xF0F0F0
-!define INSTALL_BLURB_TEXT_COLOR 0x666699
-!define INSTALL_PROGRESS_TEXT_COLOR_NORMAL 0x666699
-!define INSTALL_PROGRESS_TEXT_COLOR_FADED 0x9999C0
+!define URLUpdateInfo         "http://www.palemoon.org/unstable/"
+!define HelpLink              "http://www.palemoon.org/unstable/"
+!define URLSystemRequirements "http://www.palemoon.org/download.shtml"
diff --git a/application/palemoon/installer/windows/Makefile.in b/application/palemoon/installer/windows/Makefile.in
index 7ba70d912..9b0f697c8 100644
--- a/application/palemoon/installer/windows/Makefile.in
+++ b/application/palemoon/installer/windows/Makefile.in
@@ -79,10 +79,6 @@ $(CONFIG_DIR)/setup.exe::
 	$(PYTHON) $(topsrcdir)/toolkit/mozapps/installer/windows/nsis/preprocess-locale.py \
 	  --preprocess-locale $(topsrcdir) \
 	  $(PPL_LOCALE_ARGS) $(AB_CD) $(CONFIG_DIR)
-	$(PYTHON) $(topsrcdir)/toolkit/mozapps/installer/windows/nsis/preprocess-locale.py \
-	  --preprocess-single-file $(topsrcdir) \
-	  $(PPL_LOCALE_ARGS) $(CONFIG_DIR) \
-	  nsisstrings.properties nsisstrings.nlf
 
 GARBARGE_DIRS += instgen
 
diff --git a/application/palemoon/installer/windows/nsis/defines.nsi.in b/application/palemoon/installer/windows/nsis/defines.nsi.in
index 97422c4f6..edef802a9 100644
--- a/application/palemoon/installer/windows/nsis/defines.nsi.in
+++ b/application/palemoon/installer/windows/nsis/defines.nsi.in
@@ -3,23 +3,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-# Defining FunnelcakeVersion will append the value of StubURLVersionAppend to
-# StubURLVersion, append the value of URLManualDownloadAppend to
-# URLManualDownload, and append the value of URLStubDownloadAppend to
-# URLStubDownload. The value of FunnelcakeVersion should not be defined when it
-# is not used and when it is defined its value should never be empty.
-# !define FunnelcakeVersion        "999"
-
-!ifdef FunnelcakeVersion
-!define URLManualDownloadAppend  "&f=${FunnelcakeVersion}"
-!define URLStubDownloadAppend    "-f${FunnelcakeVersion}"
-!define StubURLVersionAppend     "-${FunnelcakeVersion}"
-!else
-!define URLManualDownloadAppend  ""
-!define URLStubDownloadAppend    ""
-!define StubURLVersionAppend     ""
-!endif
-
 # These defines should match application.ini settings
 !define AppName               "Pale Moon"
 !define AppVersion            "@APP_VERSION@"
@@ -84,13 +67,3 @@ VIAddVersionKey "FileVersion"     "${AppVersion}"
 VIAddVersionKey "ProductVersion"  "${AppVersion}"
 # Comments is not used but left below commented out for future reference
 # VIAddVersionKey "Comments"        "Comments"
-
-# Control positions in Dialog Units so they are placed correctly with
-# non-default DPI settings
-!define OPTIONS_ITEM_EDGE_DU 90u
-!define OPTIONS_ITEM_WIDTH_DU 356u
-!define OPTIONS_SUBITEM_EDGE_DU 119u
-!define OPTIONS_SUBITEM_WIDTH_DU 327u
-!define INSTALL_BLURB_TOP_DU 78u
-!define APPNAME_BMP_EDGE_DU 19u
-!define APPNAME_BMP_TOP_DU 12u
diff --git a/application/palemoon/locales/en-US/installer/nsisstrings.properties b/application/palemoon/locales/en-US/installer/nsisstrings.properties
deleted file mode 100644
index fc2898860..000000000
--- a/application/palemoon/locales/en-US/installer/nsisstrings.properties
+++ /dev/null
@@ -1,67 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-# LOCALIZATION NOTE:
-
-# This file must be saved as UTF8
-
-# Accesskeys are defined by prefixing the letter that is to be used for the
-# accesskey with an ampersand (e.g. &).
-
-# Do not replace $BrandShortName, $BrandFullName, or $BrandFullNameDA with a
-# custom string and always use the same one as used by the en-US files.
-# $BrandFullNameDA allows the string to contain an ampersand (e.g. DA stands
-# for double ampersand) and prevents the letter following the ampersand from
-# being used as an accesskey.
-
-# You can use \n to create a newline in the string but only when the string
-# from en-US contains a \n.
-
-WIN_CAPTION=$BrandShortName Setup
-
-INTRO_BLURB1=Thanks for choosing $BrandFullName, the browser that chooses you above everything else.
-INSTALL_BLURB1=You're about to enjoy the very latest in speed, flexibility and security so you're always in control.
-INSTALL_BLURB2=That's because $BrandShortName is made by a non-profit to make browsing and the Web better for you.
-INSTALL_BLURB3=You're also joining a global community of users, contributors and developers working to make the best browser in the world.
-
-WARN_MIN_SUPPORTED_OSVER_MSG=Sorry, $BrandShortName can't be installed. This version of $BrandShortName requires ${MinSupportedVer} or newer.
-WARN_MIN_SUPPORTED_CPU_MSG=Sorry, $BrandShortName can't be installed. This version of $BrandShortName requires a processor with ${MinSupportedCPU} support.
-WARN_MIN_SUPPORTED_OSVER_CPU_MSG=Sorry, $BrandShortName can't be installed. This version of $BrandShortName requires ${MinSupportedVer} or newer and a processor with ${MinSupportedCPU} support.
-WARN_WRITE_ACCESS=You don't have access to write to the installation directory.\n\nClick OK to select a different directory.
-WARN_DISK_SPACE=You don't have sufficient disk space to install to this location.\n\nClick OK to select a different location.
-WARN_ROOT_INSTALL=Unable to install to the root of your disk.\n\nClick OK to select a different location.
-WARN_MANUALLY_CLOSE_APP_LAUNCH=$BrandShortName is already running.\n\nPlease close $BrandShortName prior to launching the version you have just installed.
-
-ERROR_DOWNLOAD=Your download was interrupted.\n\nPlease click the OK button to continue.
-
-INSTALL_BUTTON=&Install
-UPGRADE_BUTTON=&Upgrade
-CANCEL_BUTTON=Cancel
-OPTIONS_BUTTON=&Options
-
-MAKE_DEFAULT=&Make $BrandShortName my default browser
-CREATE_SHORTCUTS=Create Shortcuts for $BrandShortName:
-ADD_SC_TASKBAR=On my &Task bar
-ADD_SC_QUICKLAUNCHBAR=On my &Quick Launch bar
-ADD_CheckboxShortcutInStartMenu=In my &Start Menu Programs Folder
-ADD_CheckboxShortcutOnDesktop=On my &Desktop
-SPACE_REQUIRED=Space Required:
-SPACE_AVAILABLE=Space Available:
-ONE_MOMENT_INSTALL=One moment, $BrandShortName will launch as soon as the install is complete…
-ONE_MOMENT_UPGRADE=One moment, $BrandShortName will launch as soon as the upgrade is complete…
-INSTALL_MAINT_SERVICE=&Install the $BrandShortName background update service
-SEND_PING=S&end information about this installation to Mozilla
-BROWSE_BUTTON=B&rowse…
-DEST_FOLDER=Destination Folder
-
-DOWNLOADING_LABEL=Downloading $BrandShortName…
-INSTALLING_LABEL=Installing $BrandShortName…
-UPGRADING_LABEL=Upgrading $BrandShortName…
-
-SELECT_FOLDER_TEXT=Select the folder to install $BrandShortName in.
-
-BYTE=B
-KILO=K
-MEGA=M
-GIGA=G
diff --git a/media/ffvpx/README_MCP b/media/ffvpx/README_MCP
index 4546d45a3..26834d3e3 100644
--- a/media/ffvpx/README_MCP
+++ b/media/ffvpx/README_MCP
@@ -13,9 +13,6 @@ configuration files were generated as follow using the configure script:
 config*:
 replace: /HAVE_(MALLOC_H|ARC4RANDOM|LOCALTIME_R|MEMALIGN|POSIX_MEMALIGN)/d
 
-config_darwin32.h:
-add to configure command: --disable-asm --disable-x86asm --cc='clang -m32'
-
 config_unix32.h:
 add to configure command: --disable-asm --disable-x86asm --cc='clang -m32'
 replace: s/HAVE_SYSCTL 1/HAVE_SYSCTL 0/ and s/HAVE_MEMALIGN 1/HAVE_MEMALIGN 0/ and s/HAVE_POSIX_MEMALIGN 1/HAVE_POSIX_MEMALIGN 0/
diff --git a/media/ffvpx/config.h b/media/ffvpx/config.h
index dab01e05c..fb2a3b529 100644
--- a/media/ffvpx/config.h
+++ b/media/ffvpx/config.h
@@ -27,10 +27,7 @@
 #define HAVE_LIBC_MSVCRT 0
 #endif
 #elif defined(XP_DARWIN)
-#if defined(HAVE_64BIT_BUILD)
 #include "config_darwin64.h"
-#else
-#include "config_darwin32.h"
 #endif
 #elif defined(XP_UNIX)
 #if defined(HAVE_64BIT_BUILD)
diff --git a/media/ffvpx/config_darwin32.h b/media/ffvpx/config_darwin32.h
deleted file mode 100644
index f92be8737..000000000
--- a/media/ffvpx/config_darwin32.h
+++ /dev/null
@@ -1,654 +0,0 @@
-/* Automatically generated by configure - do not modify! */
-#ifndef FFMPEG_CONFIG_H
-#define FFMPEG_CONFIG_H
-#define FFMPEG_CONFIGURATION "--disable-everything --disable-protocols --disable-demuxers --disable-muxers --disable-filters --disable-programs --disable-doc --disable-parsers --enable-parser=vp8 --enable-parser=vp9 --enable-decoder=vp8 --enable-decoder=vp9 --disable-static --enable-shared --disable-debug --disable-sdl --disable-libxcb --disable-securetransport --disable-iconv --disable-swresample --disable-swscale --disable-avdevice --disable-avfilter --disable-avformat --disable-d3d11va --disable-dxva2 --disable-vaapi --disable-vda --disable-vdpau --disable-videotoolbox --enable-asm --enable-yasm --disable-asm --disable-yasm --cc='clang -m32'"
-#define FFMPEG_LICENSE "LGPL version 2.1 or later"
-#define CONFIG_THIS_YEAR 2016
-#define FFMPEG_DATADIR "/usr/local/share/ffmpeg"
-#define AVCONV_DATADIR "/usr/local/share/ffmpeg"
-#define CC_IDENT "Apple LLVM version 7.0.2 (clang-700.1.81)"
-#define av_restrict restrict
-#define EXTERN_PREFIX "_"
-#define EXTERN_ASM _
-#define BUILDSUF ""
-#define SLIBSUF ".dylib"
-#define HAVE_MMX2 HAVE_MMXEXT
-#define SWS_MAX_FILTER_SIZE 256
-#define ARCH_AARCH64 0
-#define ARCH_ALPHA 0
-#define ARCH_ARM 0
-#define ARCH_AVR32 0
-#define ARCH_AVR32_AP 0
-#define ARCH_AVR32_UC 0
-#define ARCH_BFIN 0
-#define ARCH_IA64 0
-#define ARCH_M68K 0
-#define ARCH_MIPS 0
-#define ARCH_MIPS64 0
-#define ARCH_PARISC 0
-#define ARCH_PPC 0
-#define ARCH_PPC64 0
-#define ARCH_S390 0
-#define ARCH_SH4 0
-#define ARCH_SPARC 0
-#define ARCH_SPARC64 0
-#define ARCH_TILEGX 0
-#define ARCH_TILEPRO 0
-#define ARCH_TOMI 0
-#define ARCH_X86 0
-#define ARCH_X86_32 0
-#define ARCH_X86_64 0
-#define HAVE_ARMV5TE 0
-#define HAVE_ARMV6 0
-#define HAVE_ARMV6T2 0
-#define HAVE_ARMV8 0
-#define HAVE_NEON 0
-#define HAVE_VFP 0
-#define HAVE_VFPV3 0
-#define HAVE_SETEND 0
-#define HAVE_ALTIVEC 0
-#define HAVE_DCBZL 0
-#define HAVE_LDBRX 0
-#define HAVE_POWER8 0
-#define HAVE_PPC4XX 0
-#define HAVE_VSX 0
-#define HAVE_AESNI 0
-#define HAVE_AMD3DNOW 0
-#define HAVE_AMD3DNOWEXT 0
-#define HAVE_AVX 0
-#define HAVE_AVX2 0
-#define HAVE_FMA3 0
-#define HAVE_FMA4 0
-#define HAVE_MMX 0
-#define HAVE_MMXEXT 0
-#define HAVE_SSE 0
-#define HAVE_SSE2 0
-#define HAVE_SSE3 0
-#define HAVE_SSE4 0
-#define HAVE_SSE42 0
-#define HAVE_SSSE3 0
-#define HAVE_XOP 0
-#define HAVE_CPUNOP 0
-#define HAVE_I686 0
-#define HAVE_MIPSFPU 0
-#define HAVE_MIPS32R2 0
-#define HAVE_MIPS32R5 0
-#define HAVE_MIPS64R2 0
-#define HAVE_MIPS32R6 0
-#define HAVE_MIPS64R6 0
-#define HAVE_MIPSDSP 0
-#define HAVE_MIPSDSPR2 0
-#define HAVE_MSA 0
-#define HAVE_LOONGSON2 0
-#define HAVE_LOONGSON3 0
-#define HAVE_MMI 0
-#define HAVE_ARMV5TE_EXTERNAL 0
-#define HAVE_ARMV6_EXTERNAL 0
-#define HAVE_ARMV6T2_EXTERNAL 0
-#define HAVE_ARMV8_EXTERNAL 0
-#define HAVE_NEON_EXTERNAL 0
-#define HAVE_VFP_EXTERNAL 0
-#define HAVE_VFPV3_EXTERNAL 0
-#define HAVE_SETEND_EXTERNAL 0
-#define HAVE_ALTIVEC_EXTERNAL 0
-#define HAVE_DCBZL_EXTERNAL 0
-#define HAVE_LDBRX_EXTERNAL 0
-#define HAVE_POWER8_EXTERNAL 0
-#define HAVE_PPC4XX_EXTERNAL 0
-#define HAVE_VSX_EXTERNAL 0
-#define HAVE_AESNI_EXTERNAL 0
-#define HAVE_AMD3DNOW_EXTERNAL 0
-#define HAVE_AMD3DNOWEXT_EXTERNAL 0
-#define HAVE_AVX_EXTERNAL 0
-#define HAVE_AVX2_EXTERNAL 0
-#define HAVE_FMA3_EXTERNAL 0
-#define HAVE_FMA4_EXTERNAL 0
-#define HAVE_MMX_EXTERNAL 0
-#define HAVE_MMXEXT_EXTERNAL 0
-#define HAVE_SSE_EXTERNAL 0
-#define HAVE_SSE2_EXTERNAL 0
-#define HAVE_SSE3_EXTERNAL 0
-#define HAVE_SSE4_EXTERNAL 0
-#define HAVE_SSE42_EXTERNAL 0
-#define HAVE_SSSE3_EXTERNAL 0
-#define HAVE_XOP_EXTERNAL 0
-#define HAVE_CPUNOP_EXTERNAL 0
-#define HAVE_I686_EXTERNAL 0
-#define HAVE_MIPSFPU_EXTERNAL 0
-#define HAVE_MIPS32R2_EXTERNAL 0
-#define HAVE_MIPS32R5_EXTERNAL 0
-#define HAVE_MIPS64R2_EXTERNAL 0
-#define HAVE_MIPS32R6_EXTERNAL 0
-#define HAVE_MIPS64R6_EXTERNAL 0
-#define HAVE_MIPSDSP_EXTERNAL 0
-#define HAVE_MIPSDSPR2_EXTERNAL 0
-#define HAVE_MSA_EXTERNAL 0
-#define HAVE_LOONGSON2_EXTERNAL 0
-#define HAVE_LOONGSON3_EXTERNAL 0
-#define HAVE_MMI_EXTERNAL 0
-#define HAVE_ARMV5TE_INLINE 0
-#define HAVE_ARMV6_INLINE 0
-#define HAVE_ARMV6T2_INLINE 0
-#define HAVE_ARMV8_INLINE 0
-#define HAVE_NEON_INLINE 0
-#define HAVE_VFP_INLINE 0
-#define HAVE_VFPV3_INLINE 0
-#define HAVE_SETEND_INLINE 0
-#define HAVE_ALTIVEC_INLINE 0
-#define HAVE_DCBZL_INLINE 0
-#define HAVE_LDBRX_INLINE 0
-#define HAVE_POWER8_INLINE 0
-#define HAVE_PPC4XX_INLINE 0
-#define HAVE_VSX_INLINE 0
-#define HAVE_AESNI_INLINE 0
-#define HAVE_AMD3DNOW_INLINE 0
-#define HAVE_AMD3DNOWEXT_INLINE 0
-#define HAVE_AVX_INLINE 0
-#define HAVE_AVX2_INLINE 0
-#define HAVE_FMA3_INLINE 0
-#define HAVE_FMA4_INLINE 0
-#define HAVE_MMX_INLINE 0
-#define HAVE_MMXEXT_INLINE 0
-#define HAVE_SSE_INLINE 0
-#define HAVE_SSE2_INLINE 0
-#define HAVE_SSE3_INLINE 0
-#define HAVE_SSE4_INLINE 0
-#define HAVE_SSE42_INLINE 0
-#define HAVE_SSSE3_INLINE 0
-#define HAVE_XOP_INLINE 0
-#define HAVE_CPUNOP_INLINE 0
-#define HAVE_I686_INLINE 0
-#define HAVE_MIPSFPU_INLINE 0
-#define HAVE_MIPS32R2_INLINE 0
-#define HAVE_MIPS32R5_INLINE 0
-#define HAVE_MIPS64R2_INLINE 0
-#define HAVE_MIPS32R6_INLINE 0
-#define HAVE_MIPS64R6_INLINE 0
-#define HAVE_MIPSDSP_INLINE 0
-#define HAVE_MIPSDSPR2_INLINE 0
-#define HAVE_MSA_INLINE 0
-#define HAVE_LOONGSON2_INLINE 0
-#define HAVE_LOONGSON3_INLINE 0
-#define HAVE_MMI_INLINE 0
-#define HAVE_ALIGNED_STACK 0
-#define HAVE_FAST_64BIT 0
-#define HAVE_FAST_CLZ 0
-#define HAVE_FAST_CMOV 0
-#define HAVE_LOCAL_ALIGNED_8 1
-#define HAVE_LOCAL_ALIGNED_16 1
-#define HAVE_LOCAL_ALIGNED_32 1
-#define HAVE_SIMD_ALIGN_16 0
-#define HAVE_ATOMICS_GCC 1
-#define HAVE_ATOMICS_SUNCC 0
-#define HAVE_ATOMICS_WIN32 0
-#define HAVE_ATOMIC_CAS_PTR 0
-#define HAVE_ATOMIC_COMPARE_EXCHANGE 1
-#define HAVE_MACHINE_RW_BARRIER 0
-#define HAVE_MEMORYBARRIER 0
-#define HAVE_MM_EMPTY 1
-#define HAVE_RDTSC 0
-#define HAVE_SARESTART 1
-#define HAVE_SEM_TIMEDWAIT 1
-#define HAVE_SYNC_VAL_COMPARE_AND_SWAP 1
-#define HAVE_CABS 1
-#define HAVE_CEXP 1
-#define HAVE_INLINE_ASM 1
-#define HAVE_SYMVER 1
-#define HAVE_YASM 0
-#define HAVE_BIGENDIAN 0
-#define HAVE_FAST_UNALIGNED 0
-#define HAVE_ALSA_ASOUNDLIB_H 0
-#define HAVE_ALTIVEC_H 0
-#define HAVE_ARPA_INET_H 1
-#define HAVE_ASM_TYPES_H 0
-#define HAVE_CDIO_PARANOIA_H 0
-#define HAVE_CDIO_PARANOIA_PARANOIA_H 0
-#define HAVE_DISPATCH_DISPATCH_H 0
-#define HAVE_DEV_BKTR_IOCTL_BT848_H 0
-#define HAVE_DEV_BKTR_IOCTL_METEOR_H 0
-#define HAVE_DEV_IC_BT8XX_H 0
-#define HAVE_DEV_VIDEO_BKTR_IOCTL_BT848_H 0
-#define HAVE_DEV_VIDEO_METEOR_IOCTL_METEOR_H 0
-#define HAVE_DIRECT_H 0
-#define HAVE_DIRENT_H 1
-#define HAVE_DLFCN_H 1
-#define HAVE_D3D11_H 0
-#define HAVE_DXVA_H 0
-#define HAVE_ES2_GL_H 0
-#define HAVE_GSM_H 0
-#define HAVE_IO_H 0
-#define HAVE_MACH_MACH_TIME_H 1
-#define HAVE_MACHINE_IOCTL_BT848_H 0
-#define HAVE_MACHINE_IOCTL_METEOR_H 0
-#define HAVE_OPENCV2_CORE_CORE_C_H 0
-#define HAVE_OPENJPEG_2_1_OPENJPEG_H 0
-#define HAVE_OPENJPEG_2_0_OPENJPEG_H 0
-#define HAVE_OPENJPEG_1_5_OPENJPEG_H 0
-#define HAVE_OPENGL_GL3_H 0
-#define HAVE_POLL_H 1
-#define HAVE_SNDIO_H 0
-#define HAVE_SOUNDCARD_H 0
-#define HAVE_SYS_MMAN_H 1
-#define HAVE_SYS_PARAM_H 1
-#define HAVE_SYS_RESOURCE_H 1
-#define HAVE_SYS_SELECT_H 1
-#define HAVE_SYS_SOUNDCARD_H 0
-#define HAVE_SYS_TIME_H 1
-#define HAVE_SYS_UN_H 1
-#define HAVE_SYS_VIDEOIO_H 0
-#define HAVE_TERMIOS_H 1
-#define HAVE_UDPLITE_H 0
-#define HAVE_UNISTD_H 1
-#define HAVE_VALGRIND_VALGRIND_H 0
-#define HAVE_WINDOWS_H 0
-#define HAVE_WINSOCK2_H 0
-#define HAVE_INTRINSICS_NEON 0
-#define HAVE_ATANF 1
-#define HAVE_ATAN2F 1
-#define HAVE_CBRT 1
-#define HAVE_CBRTF 1
-#define HAVE_COPYSIGN 1
-#define HAVE_COSF 1
-#define HAVE_ERF 1
-#define HAVE_EXP2 1
-#define HAVE_EXP2F 1
-#define HAVE_EXPF 1
-#define HAVE_HYPOT 1
-#define HAVE_ISFINITE 1
-#define HAVE_ISINF 1
-#define HAVE_ISNAN 1
-#define HAVE_LDEXPF 1
-#define HAVE_LLRINT 1
-#define HAVE_LLRINTF 1
-#define HAVE_LOG2 1
-#define HAVE_LOG2F 1
-#define HAVE_LOG10F 1
-#define HAVE_LRINT 1
-#define HAVE_LRINTF 1
-#define HAVE_POWF 1
-#define HAVE_RINT 1
-#define HAVE_ROUND 1
-#define HAVE_ROUNDF 1
-#define HAVE_SINF 1
-#define HAVE_TRUNC 1
-#define HAVE_TRUNCF 1
-#define HAVE_ACCESS 1
-#define HAVE_ALIGNED_MALLOC 0
-#define HAVE_CLOCK_GETTIME 0
-#define HAVE_CLOSESOCKET 0
-#define HAVE_COMMANDLINETOARGVW 0
-#define HAVE_COTASKMEMFREE 0
-#define HAVE_CRYPTGENRANDOM 0
-#define HAVE_DLOPEN 1
-#define HAVE_FCNTL 1
-#define HAVE_FLT_LIM 1
-#define HAVE_FORK 1
-#define HAVE_GETADDRINFO 1
-#define HAVE_GETHRTIME 0
-#define HAVE_GETOPT 1
-#define HAVE_GETPROCESSAFFINITYMASK 0
-#define HAVE_GETPROCESSMEMORYINFO 0
-#define HAVE_GETPROCESSTIMES 0
-#define HAVE_GETRUSAGE 1
-#define HAVE_GETSYSTEMTIMEASFILETIME 0
-#define HAVE_GETTIMEOFDAY 1
-#define HAVE_GLOB 1
-#define HAVE_GLXGETPROCADDRESS 0
-#define HAVE_GMTIME_R 1
-#define HAVE_INET_ATON 1
-#define HAVE_ISATTY 1
-#define HAVE_JACK_PORT_GET_LATENCY_RANGE 0
-#define HAVE_KBHIT 0
-#define HAVE_LOADLIBRARY 0
-#define HAVE_LSTAT 1
-#define HAVE_LZO1X_999_COMPRESS 0
-#define HAVE_MACH_ABSOLUTE_TIME 1
-#define HAVE_MAPVIEWOFFILE 0
-#define HAVE_MKSTEMP 1
-#define HAVE_MMAP 1
-#define HAVE_MPROTECT 1
-#define HAVE_NANOSLEEP 1
-#define HAVE_PEEKNAMEDPIPE 0
-#define HAVE_PTHREAD_CANCEL 1
-#define HAVE_SCHED_GETAFFINITY 0
-#define HAVE_SETCONSOLETEXTATTRIBUTE 0
-#define HAVE_SETCONSOLECTRLHANDLER 0
-#define HAVE_SETMODE 0
-#define HAVE_SETRLIMIT 1
-#define HAVE_SLEEP 0
-#define HAVE_STRERROR_R 1
-#define HAVE_SYSCONF 1
-#define HAVE_USLEEP 1
-#define HAVE_UTGETOSTYPEFROMSTRING 1
-#define HAVE_VIRTUALALLOC 0
-#define HAVE_WGLGETPROCADDRESS 0
-#define HAVE_PTHREADS 1
-#define HAVE_OS2THREADS 0
-#define HAVE_W32THREADS 0
-#define HAVE_AS_DN_DIRECTIVE 0
-#define HAVE_AS_FUNC 0
-#define HAVE_AS_OBJECT_ARCH 0
-#define HAVE_ASM_MOD_Q 0
-#define HAVE_ATTRIBUTE_MAY_ALIAS 1
-#define HAVE_ATTRIBUTE_PACKED 1
-#define HAVE_EBP_AVAILABLE 1
-#define HAVE_EBX_AVAILABLE 1
-#define HAVE_GNU_AS 0
-#define HAVE_GNU_WINDRES 0
-#define HAVE_IBM_ASM 0
-#define HAVE_INLINE_ASM_DIRECT_SYMBOL_REFS 1
-#define HAVE_INLINE_ASM_LABELS 1
-#define HAVE_INLINE_ASM_NONLOCAL_LABELS 1
-#define HAVE_PRAGMA_DEPRECATED 1
-#define HAVE_RSYNC_CONTIMEOUT 0
-#define HAVE_SYMVER_ASM_LABEL 1
-#define HAVE_SYMVER_GNU_ASM 0
-#define HAVE_VFP_ARGS 0
-#define HAVE_XFORM_ASM 0
-#define HAVE_XMM_CLOBBERS 1
-#define HAVE_CONDITION_VARIABLE_PTR 0
-#define HAVE_SOCKLEN_T 1
-#define HAVE_STRUCT_ADDRINFO 1
-#define HAVE_STRUCT_GROUP_SOURCE_REQ 1
-#define HAVE_STRUCT_IP_MREQ_SOURCE 1
-#define HAVE_STRUCT_IPV6_MREQ 1
-#define HAVE_STRUCT_MSGHDR_MSG_FLAGS 1
-#define HAVE_STRUCT_POLLFD 1
-#define HAVE_STRUCT_RUSAGE_RU_MAXRSS 1
-#define HAVE_STRUCT_SCTP_EVENT_SUBSCRIBE 0
-#define HAVE_STRUCT_SOCKADDR_IN6 1
-#define HAVE_STRUCT_SOCKADDR_SA_LEN 1
-#define HAVE_STRUCT_SOCKADDR_STORAGE 1
-#define HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC 0
-#define HAVE_STRUCT_V4L2_FRMIVALENUM_DISCRETE 0
-#define HAVE_ATOMICS_NATIVE 1
-#define HAVE_DOS_PATHS 0
-#define HAVE_DXVA2_LIB 0
-#define HAVE_DXVA2API_COBJ 0
-#define HAVE_LIBC_MSVCRT 0
-#define HAVE_LIBDC1394_1 0
-#define HAVE_LIBDC1394_2 0
-#define HAVE_MAKEINFO 1
-#define HAVE_MAKEINFO_HTML 1
-#define HAVE_MMAL_PARAMETER_VIDEO_MAX_NUM_CALLBACKS 0
-#define HAVE_PERL 1
-#define HAVE_POD2MAN 1
-#define HAVE_SDL2 0
-#define HAVE_SECTION_DATA_REL_RO 0
-#define HAVE_TEXI2HTML 0
-#define HAVE_THREADS 1
-#define HAVE_VAAPI_DRM 0
-#define HAVE_VAAPI_X11 0
-#define HAVE_VDPAU_X11 0
-#define HAVE_WINRT 0
-#define HAVE_XLIB 0
-#define CONFIG_BSFS 0
-#define CONFIG_DECODERS 1
-#define CONFIG_PARSERS 1
-#define CONFIG_DOC 0
-#define CONFIG_HTMLPAGES 1
-#define CONFIG_MANPAGES 1
-#define CONFIG_PODPAGES 1
-#define CONFIG_TXTPAGES 1
-#define CONFIG_AVIO_DIR_CMD_EXAMPLE 1
-#define CONFIG_AVIO_READING_EXAMPLE 1
-#define CONFIG_DECODING_ENCODING_EXAMPLE 0
-#define CONFIG_DEMUXING_DECODING_EXAMPLE 0
-#define CONFIG_EXTRACT_MVS_EXAMPLE 0
-#define CONFIG_FILTER_AUDIO_EXAMPLE 0
-#define CONFIG_FILTERING_AUDIO_EXAMPLE 0
-#define CONFIG_FILTERING_VIDEO_EXAMPLE 0
-#define CONFIG_HTTP_MULTICLIENT_EXAMPLE 0
-#define CONFIG_METADATA_EXAMPLE 0
-#define CONFIG_MUXING_EXAMPLE 0
-#define CONFIG_QSVDEC_EXAMPLE 0
-#define CONFIG_REMUXING_EXAMPLE 0
-#define CONFIG_RESAMPLING_AUDIO_EXAMPLE 0
-#define CONFIG_SCALING_VIDEO_EXAMPLE 0
-#define CONFIG_TRANSCODE_AAC_EXAMPLE 0
-#define CONFIG_TRANSCODING_EXAMPLE 0
-#define CONFIG_AVISYNTH 0
-#define CONFIG_BZLIB 0
-#define CONFIG_CHROMAPRINT 0
-#define CONFIG_CRYSTALHD 0
-#define CONFIG_DECKLINK 0
-#define CONFIG_FREI0R 0
-#define CONFIG_GCRYPT 0
-#define CONFIG_GMP 0
-#define CONFIG_GNUTLS 0
-#define CONFIG_ICONV 0
-#define CONFIG_JNI 0
-#define CONFIG_LADSPA 0
-#define CONFIG_LIBASS 0
-#define CONFIG_LIBBLURAY 0
-#define CONFIG_LIBBS2B 0
-#define CONFIG_LIBCACA 0
-#define CONFIG_LIBCDIO 0
-#define CONFIG_LIBCELT 0
-#define CONFIG_LIBDC1394 0
-#define CONFIG_LIBEBUR128 0
-#define CONFIG_LIBFDK_AAC 0
-#define CONFIG_LIBFLITE 0
-#define CONFIG_LIBFONTCONFIG 0
-#define CONFIG_LIBFREETYPE 0
-#define CONFIG_LIBFRIBIDI 0
-#define CONFIG_LIBGME 0
-#define CONFIG_LIBGSM 0
-#define CONFIG_LIBIEC61883 0
-#define CONFIG_LIBILBC 0
-#define CONFIG_LIBKVAZAAR 0
-#define CONFIG_LIBMODPLUG 0
-#define CONFIG_LIBMP3LAME 0
-#define CONFIG_LIBNUT 0
-#define CONFIG_LIBOPENCORE_AMRNB 0
-#define CONFIG_LIBOPENCORE_AMRWB 0
-#define CONFIG_LIBOPENCV 0
-#define CONFIG_LIBOPENH264 0
-#define CONFIG_LIBOPENJPEG 0
-#define CONFIG_LIBOPENMPT 0
-#define CONFIG_LIBOPUS 0
-#define CONFIG_LIBPULSE 0
-#define CONFIG_LIBRTMP 0
-#define CONFIG_LIBRUBBERBAND 0
-#define CONFIG_LIBSCHROEDINGER 0
-#define CONFIG_LIBSHINE 0
-#define CONFIG_LIBSMBCLIENT 0
-#define CONFIG_LIBSNAPPY 0
-#define CONFIG_LIBSOXR 0
-#define CONFIG_LIBSPEEX 0
-#define CONFIG_LIBSSH 0
-#define CONFIG_LIBTESSERACT 0
-#define CONFIG_LIBTHEORA 0
-#define CONFIG_LIBTWOLAME 0
-#define CONFIG_LIBV4L2 0
-#define CONFIG_LIBVIDSTAB 0
-#define CONFIG_LIBVO_AMRWBENC 0
-#define CONFIG_LIBVORBIS 0
-#define CONFIG_LIBVPX 0
-#define CONFIG_LIBWAVPACK 0
-#define CONFIG_LIBWEBP 0
-#define CONFIG_LIBX264 0
-#define CONFIG_LIBX265 0
-#define CONFIG_LIBXAVS 0
-#define CONFIG_LIBXCB 0
-#define CONFIG_LIBXCB_SHM 0
-#define CONFIG_LIBXCB_SHAPE 0
-#define CONFIG_LIBXCB_XFIXES 0
-#define CONFIG_LIBXVID 0
-#define CONFIG_LIBZIMG 0
-#define CONFIG_LIBZMQ 0
-#define CONFIG_LIBZVBI 0
-#define CONFIG_LZMA 0
-#define CONFIG_MEDIACODEC 0
-#define CONFIG_NETCDF 0
-#define CONFIG_OPENAL 0
-#define CONFIG_OPENCL 0
-#define CONFIG_OPENGL 0
-#define CONFIG_OPENSSL 0
-#define CONFIG_SCHANNEL 0
-#define CONFIG_SDL 0
-#define CONFIG_SDL2 0
-#define CONFIG_SECURETRANSPORT 0
-#define CONFIG_VIDEOTOOLBOX 0
-#define CONFIG_X11GRAB 0
-#define CONFIG_XLIB 0
-#define CONFIG_ZLIB 0
-#define CONFIG_AUDIOTOOLBOX 0
-#define CONFIG_CUDA 0
-#define CONFIG_CUVID 0
-#define CONFIG_D3D11VA 0
-#define CONFIG_DXVA2 0
-#define CONFIG_LIBMFX 0
-#define CONFIG_LIBNPP 0
-#define CONFIG_MMAL 0
-#define CONFIG_NVENC 0
-#define CONFIG_OMX 0
-#define CONFIG_VAAPI 0
-#define CONFIG_VDA 0
-#define CONFIG_VDPAU 0
-#define CONFIG_XVMC 0
-#define CONFIG_FTRAPV 0
-#define CONFIG_GRAY 0
-#define CONFIG_HARDCODED_TABLES 0
-#define CONFIG_OMX_RPI 0
-#define CONFIG_RUNTIME_CPUDETECT 1
-#define CONFIG_SAFE_BITSTREAM_READER 1
-#define CONFIG_SHARED 1
-#define CONFIG_SMALL 0
-#define CONFIG_STATIC 0
-#define CONFIG_SWSCALE_ALPHA 1
-#define CONFIG_GPL 0
-#define CONFIG_NONFREE 0
-#define CONFIG_VERSION3 0
-#define CONFIG_AVCODEC 1
-#define CONFIG_AVDEVICE 0
-#define CONFIG_AVFILTER 0
-#define CONFIG_AVFORMAT 0
-#define CONFIG_AVRESAMPLE 0
-#define CONFIG_AVUTIL 1
-#define CONFIG_POSTPROC 0
-#define CONFIG_SWRESAMPLE 0
-#define CONFIG_SWSCALE 0
-#define CONFIG_FFPLAY 0
-#define CONFIG_FFPROBE 0
-#define CONFIG_FFSERVER 0
-#define CONFIG_FFMPEG 0
-#define CONFIG_DCT 0
-#define CONFIG_DWT 0
-#define CONFIG_ERROR_RESILIENCE 0
-#define CONFIG_FAAN 1
-#define CONFIG_FAST_UNALIGNED 0
-#define CONFIG_FFT 0
-#define CONFIG_LSP 0
-#define CONFIG_LZO 0
-#define CONFIG_MDCT 0
-#define CONFIG_PIXELUTILS 0
-#define CONFIG_NETWORK 0
-#define CONFIG_RDFT 0
-#define CONFIG_FONTCONFIG 0
-#define CONFIG_MEMALIGN_HACK 0
-#define CONFIG_MEMORY_POISONING 0
-#define CONFIG_NEON_CLOBBER_TEST 0
-#define CONFIG_PIC 1
-#define CONFIG_POD2MAN 1
-#define CONFIG_RAISE_MAJOR 0
-#define CONFIG_THUMB 0
-#define CONFIG_VALGRIND_BACKTRACE 0
-#define CONFIG_XMM_CLOBBER_TEST 0
-#define CONFIG_AANDCTTABLES 0
-#define CONFIG_AC3DSP 0
-#define CONFIG_AUDIO_FRAME_QUEUE 0
-#define CONFIG_AUDIODSP 0
-#define CONFIG_BLOCKDSP 0
-#define CONFIG_BSWAPDSP 0
-#define CONFIG_CABAC 0
-#define CONFIG_DIRAC_PARSE 0
-#define CONFIG_DVPROFILE 0
-#define CONFIG_EXIF 0
-#define CONFIG_FAANDCT 0
-#define CONFIG_FAANIDCT 0
-#define CONFIG_FDCTDSP 0
-#define CONFIG_FLACDSP 1
-#define CONFIG_FMTCONVERT 0
-#define CONFIG_G722DSP 0
-#define CONFIG_GOLOMB 1
-#define CONFIG_GPLV3 0
-#define CONFIG_H263DSP 0
-#define CONFIG_H264CHROMA 0
-#define CONFIG_H264DSP 0
-#define CONFIG_H264PRED 1
-#define CONFIG_H264QPEL 0
-#define CONFIG_HPELDSP 0
-#define CONFIG_HUFFMAN 0
-#define CONFIG_HUFFYUVDSP 0
-#define CONFIG_HUFFYUVENCDSP 0
-#define CONFIG_IDCTDSP 0
-#define CONFIG_IIRFILTER 0
-#define CONFIG_IMDCT15 0
-#define CONFIG_INTRAX8 0
-#define CONFIG_ISO_MEDIA 0
-#define CONFIG_IVIDSP 0
-#define CONFIG_JPEGTABLES 0
-#define CONFIG_LGPLV3 0
-#define CONFIG_LIBX262 0
-#define CONFIG_LLAUDDSP 0
-#define CONFIG_LLVIDDSP 0
-#define CONFIG_LPC 0
-#define CONFIG_LZF 0
-#define CONFIG_ME_CMP 0
-#define CONFIG_MPEG_ER 0
-#define CONFIG_MPEGAUDIO 0
-#define CONFIG_MPEGAUDIODSP 0
-#define CONFIG_MPEGVIDEO 0
-#define CONFIG_MPEGVIDEOENC 0
-#define CONFIG_MSS34DSP 0
-#define CONFIG_PIXBLOCKDSP 0
-#define CONFIG_QPELDSP 0
-#define CONFIG_QSV 0
-#define CONFIG_QSVDEC 0
-#define CONFIG_QSVENC 0
-#define CONFIG_RANGECODER 0
-#define CONFIG_RIFFDEC 0
-#define CONFIG_RIFFENC 0
-#define CONFIG_RTPDEC 0
-#define CONFIG_RTPENC_CHAIN 0
-#define CONFIG_RV34DSP 0
-#define CONFIG_SINEWIN 0
-#define CONFIG_SNAPPY 0
-#define CONFIG_SRTP 0
-#define CONFIG_STARTCODE 0
-#define CONFIG_TEXTUREDSP 0
-#define CONFIG_TEXTUREDSPENC 0
-#define CONFIG_TPELDSP 0
-#define CONFIG_VAAPI_ENCODE 0
-#define CONFIG_VC1DSP 0
-#define CONFIG_VIDEODSP 1
-#define CONFIG_VP3DSP 0
-#define CONFIG_VP56DSP 0
-#define CONFIG_VP8DSP 1
-#define CONFIG_VT_BT2020 0
-#define CONFIG_WMA_FREQS 0
-#define CONFIG_WMV2DSP 0
-#define CONFIG_AAC_ADTSTOASC_BSF 0
-#define CONFIG_CHOMP_BSF 0
-#define CONFIG_DUMP_EXTRADATA_BSF 0
-#define CONFIG_DCA_CORE_BSF 0
-#define CONFIG_H264_MP4TOANNEXB_BSF 0
-#define CONFIG_HEVC_MP4TOANNEXB_BSF 0
-#define CONFIG_IMX_DUMP_HEADER_BSF 0
-#define CONFIG_MJPEG2JPEG_BSF 0
-#define CONFIG_MJPEGA_DUMP_HEADER_BSF 0
-#define CONFIG_MP3_HEADER_DECOMPRESS_BSF 0
-#define CONFIG_MPEG4_UNPACK_BFRAMES_BSF 0
-#define CONFIG_MOV2TEXTSUB_BSF 0
-#define CONFIG_NOISE_BSF 0
-#define CONFIG_REMOVE_EXTRADATA_BSF 0
-#define CONFIG_TEXT2MOVSUB_BSF 0
-#define CONFIG_VP9_SUPERFRAME_BSF 0
-#define CONFIG_VP8_DECODER 1
-#define CONFIG_VP9_DECODER 1
-#define CONFIG_FLAC_DECODER 1
-#define CONFIG_FLAC_PARSER 1
-#define CONFIG_VP8_PARSER 1
-#define CONFIG_VP9_PARSER 1
-#endif /* FFMPEG_CONFIG_H */
diff --git a/media/ffvpx/ffvpxcommon.mozbuild b/media/ffvpx/ffvpxcommon.mozbuild
index 620158694..b6230bb9f 100644
--- a/media/ffvpx/ffvpxcommon.mozbuild
+++ b/media/ffvpx/ffvpxcommon.mozbuild
@@ -21,7 +21,7 @@ if CONFIG['FFVPX_ASFLAGS']:
         else:
             ASFLAGS += ['-Pconfig_win64.asm']
     elif CONFIG['OS_ARCH'] == 'Darwin':
-        # 32/64-bit macosx assemblers need to prefix symbols with an underscore.
+        # 64-bit macosx assemblers need to prefix symbols with an underscore.
         ASFLAGS += [
             '-Pconfig_darwin64.asm',
             '-DPREFIX'
diff --git a/mfbt/Casting.h b/mfbt/Casting.h
index a7d0fb50d..adf2c9045 100644
--- a/mfbt/Casting.h
+++ b/mfbt/Casting.h
@@ -238,6 +238,19 @@ AssertedCast(const From aFrom)
   return static_cast<To>(aFrom);
 }
 
+/**
+ * Cast a value of integral type |From| to a value of integral type |To|,
+ * release asserting that the cast will be a safe cast per C++ (that is, that
+ * |to| is in the range of values permitted for the type |From|).
+ */
+template<typename To, typename From>
+inline To
+ReleaseAssertedCast(const From aFrom)
+{
+  MOZ_RELEASE_ASSERT((detail::IsInBounds<From, To>(aFrom)));
+  return static_cast<To>(aFrom);
+}
+
 } // namespace mozilla
 
 #endif /* mozilla_Casting_h */
diff --git a/mfbt/Range.h b/mfbt/Range.h
index 47d91bb0c..753fe07f8 100644
--- a/mfbt/Range.h
+++ b/mfbt/Range.h
@@ -9,6 +9,7 @@
 
 #include "mozilla/RangedPtr.h"
 #include "mozilla/TypeTraits.h"
+#include "mozilla/Span.h"
 
 #include <stddef.h>
 
@@ -44,6 +45,19 @@ public:
       mEnd(aOther.mEnd)
   {}
 
+  MOZ_IMPLICIT Range(Span<T> aSpan)
+    : Range(aSpan.Elements(), aSpan.Length())
+  {
+  }
+
+  template<typename U,
+           class = typename EnableIf<IsConvertible<U (*)[], T (*)[]>::value,
+                                     int>::Type>
+  MOZ_IMPLICIT Range(const Span<U>& aSpan)
+    : Range(aSpan.Elements(), aSpan.Length())
+  {
+  }
+
   RangedPtr<T> begin() const { return mStart; }
   RangedPtr<T> end() const { return mEnd; }
   size_t length() const { return mEnd - mStart; }
@@ -51,8 +65,26 @@ public:
   T& operator[](size_t aOffset) const { return mStart[aOffset]; }
 
   explicit operator bool() const { return mStart != nullptr; }
+
+  operator Span<T>() { return Span<T>(mStart.get(), length()); }
+
+  operator Span<const T>() const { return Span<T>(mStart.get(), length()); }
 };
 
+template<class T>
+Span<T>
+MakeSpan(Range<T>& aRange)
+{
+  return aRange;
+}
+
+template<class T>
+Span<const T>
+MakeSpan(const Range<T>& aRange)
+{
+  return aRange;
+}
+
 } // namespace mozilla
 
 #endif /* mozilla_Range_h */
diff --git a/mfbt/Span.h b/mfbt/Span.h
new file mode 100644
index 000000000..f031a928b
--- /dev/null
+++ b/mfbt/Span.h
@@ -0,0 +1,1041 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+// Adapted from https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/include/gsl/span
+// and https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/include/gsl/gsl_util
+
+#ifndef mozilla_Span_h
+#define mozilla_Span_h
+
+#include "mozilla/Array.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Casting.h"
+#include "mozilla/IntegerTypeTraits.h"
+#include "mozilla/Move.h"
+#include "mozilla/TypeTraits.h"
+#include "mozilla/UniquePtr.h"
+
+#include <algorithm>
+#include <array>
+#include <cstring>
+#include <iterator>
+
+// Classifications for reasons why constexpr was removed in C++14 to C++11
+// conversion. Once we upgrade compilers, we can try defining each of these
+// to constexpr to restore a category of constexprs at a time.
+#define MOZ_SPAN_ASSERTION_CONSTEXPR
+#define MOZ_SPAN_GCC_CONSTEXPR
+#define MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR
+#define MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN
+#define MOZ_SPAN_NON_CONST_CONSTEXPR
+
+#ifdef _MSC_VER
+#pragma warning(push)
+
+// turn off some warnings that are noisy about our MOZ_RELEASE_ASSERT statements
+#pragma warning(disable : 4127) // conditional expression is constant
+
+// blanket turn off warnings from CppCoreCheck for now
+// so people aren't annoyed by them when running the tool.
+// more targeted suppressions will be added in a future update to the GSL
+#pragma warning(disable : 26481 26482 26483 26485 26490 26491 26492 26493 26495)
+
+#if _MSC_VER < 1910
+#pragma push_macro("constexpr")
+#define constexpr /*constexpr*/
+
+#endif            // _MSC_VER < 1910
+#endif            // _MSC_VER
+
+namespace mozilla {
+
+// Stuff from gsl_util
+
+// narrow_cast(): a searchable way to do narrowing casts of values
+template<class T, class U>
+inline constexpr T
+narrow_cast(U&& u)
+{
+  return static_cast<T>(mozilla::Forward<U>(u));
+}
+
+// end gsl_util
+
+// [views.constants], constants
+// This was -1 in gsl::span, but using size_t for sizes instead of ptrdiff_t
+// and reserving a magic value that realistically doesn't occur in
+// compile-time-constant Span sizes makes things a lot less messy in terms of
+// comparison between signed and unsigned.
+constexpr const size_t dynamic_extent = mozilla::MaxValue<size_t>::value;
+
+template<class ElementType, size_t Extent = dynamic_extent>
+class Span;
+
+// implementation details
+namespace span_details {
+
+// C++14 types that we don't have because we build as C++11.
+template<class T>
+using remove_cv_t = typename mozilla::RemoveCV<T>::Type;
+template<class T>
+using remove_const_t = typename mozilla::RemoveConst<T>::Type;
+template<bool B, class T, class F>
+using conditional_t = typename mozilla::Conditional<B, T, F>::Type;
+template<class T>
+using add_pointer_t = typename mozilla::AddPointer<T>::Type;
+template<bool B, class T = void>
+using enable_if_t = typename mozilla::EnableIf<B, T>::Type;
+
+template<class T>
+struct is_span_oracle : mozilla::FalseType
+{
+};
+
+template<class ElementType, size_t Extent>
+struct is_span_oracle<mozilla::Span<ElementType, Extent>> : mozilla::TrueType
+{
+};
+
+template<class T>
+struct is_span : public is_span_oracle<remove_cv_t<T>>
+{
+};
+
+template<class T>
+struct is_std_array_oracle : mozilla::FalseType
+{
+};
+
+template<class ElementType, size_t Extent>
+struct is_std_array_oracle<std::array<ElementType, Extent>> : mozilla::TrueType
+{
+};
+
+template<class T>
+struct is_std_array : public is_std_array_oracle<remove_cv_t<T>>
+{
+};
+
+template<size_t From, size_t To>
+struct is_allowed_extent_conversion
+  : public mozilla::IntegralConstant<bool,
+                                  From == To ||
+                                    From == mozilla::dynamic_extent ||
+                                    To == mozilla::dynamic_extent>
+{
+};
+
+template<class From, class To>
+struct is_allowed_element_type_conversion
+  : public mozilla::IntegralConstant<bool, mozilla::IsConvertible<From (*)[], To (*)[]>::value>
+{
+};
+
+template<class Span, bool IsConst>
+class span_iterator
+{
+  using element_type_ = typename Span::element_type;
+
+public:
+  using iterator_category = std::random_access_iterator_tag;
+  using value_type = remove_const_t<element_type_>;
+  using difference_type = typename Span::index_type;
+
+  using reference = conditional_t<IsConst, const element_type_, element_type_>&;
+  using pointer = add_pointer_t<reference>;
+
+  constexpr span_iterator() : span_iterator(nullptr, 0) {}
+
+  MOZ_SPAN_ASSERTION_CONSTEXPR span_iterator(const Span* span,
+                                             typename Span::index_type index)
+    : span_(span)
+    , index_(index)
+  {
+    MOZ_RELEASE_ASSERT(span == nullptr ||
+                       (index_ >= 0 && index <= span_->Length()));
+  }
+
+  friend class span_iterator<Span, true>;
+  constexpr MOZ_IMPLICIT span_iterator(const span_iterator<Span, false>& other)
+    : span_iterator(other.span_, other.index_)
+  {
+  }
+
+  MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR span_iterator<Span, IsConst>&
+  operator=(const span_iterator<Span, IsConst>&) = default;
+
+  MOZ_SPAN_GCC_CONSTEXPR reference operator*() const
+  {
+    MOZ_RELEASE_ASSERT(span_);
+    return (*span_)[index_];
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR pointer operator->() const
+  {
+    MOZ_RELEASE_ASSERT(span_);
+    return &((*span_)[index_]);
+  }
+
+  MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator& operator++()
+  {
+    MOZ_RELEASE_ASSERT(span_ && index_ >= 0 && index_ < span_->Length());
+    ++index_;
+    return *this;
+  }
+
+  MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator operator++(int)
+  {
+    auto ret = *this;
+    ++(*this);
+    return ret;
+  }
+
+  MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator& operator--()
+  {
+    MOZ_RELEASE_ASSERT(span_ && index_ > 0 && index_ <= span_->Length());
+    --index_;
+    return *this;
+  }
+
+  MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator operator--(int)
+  {
+    auto ret = *this;
+    --(*this);
+    return ret;
+  }
+
+  MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN span_iterator
+  operator+(difference_type n) const
+  {
+    auto ret = *this;
+    return ret += n;
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR span_iterator& operator+=(difference_type n)
+  {
+    MOZ_RELEASE_ASSERT(span_ && (index_ + n) >= 0 &&
+                       (index_ + n) <= span_->Length());
+    index_ += n;
+    return *this;
+  }
+
+  MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN span_iterator
+  operator-(difference_type n) const
+  {
+    auto ret = *this;
+    return ret -= n;
+  }
+
+  MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator& operator-=(difference_type n)
+
+  {
+    return *this += -n;
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR difference_type
+  operator-(const span_iterator& rhs) const
+  {
+    MOZ_RELEASE_ASSERT(span_ == rhs.span_);
+    return index_ - rhs.index_;
+  }
+
+  constexpr reference operator[](difference_type n) const
+  {
+    return *(*this + n);
+  }
+
+  constexpr friend bool operator==(const span_iterator& lhs,
+                                   const span_iterator& rhs)
+  {
+    return lhs.span_ == rhs.span_ && lhs.index_ == rhs.index_;
+  }
+
+  constexpr friend bool operator!=(const span_iterator& lhs,
+                                   const span_iterator& rhs)
+  {
+    return !(lhs == rhs);
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR friend bool operator<(const span_iterator& lhs,
+                                               const span_iterator& rhs)
+  {
+    MOZ_RELEASE_ASSERT(lhs.span_ == rhs.span_);
+    return lhs.index_ < rhs.index_;
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR friend bool operator<=(const span_iterator& lhs,
+                                                const span_iterator& rhs)
+  {
+    return !(rhs < lhs);
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR friend bool operator>(const span_iterator& lhs,
+                                               const span_iterator& rhs)
+  {
+    return rhs < lhs;
+  }
+
+  MOZ_SPAN_GCC_CONSTEXPR friend bool operator>=(const span_iterator& lhs,
+                                                const span_iterator& rhs)
+  {
+    return !(rhs > lhs);
+  }
+
+  void swap(span_iterator& rhs)
+  {
+    std::swap(index_, rhs.index_);
+    std::swap(span_, rhs.span_);
+  }
+
+protected:
+  const Span* span_;
+  size_t index_;
+};
+
+template<class Span, bool IsConst>
+inline constexpr span_iterator<Span, IsConst>
+operator+(typename span_iterator<Span, IsConst>::difference_type n,
+          const span_iterator<Span, IsConst>& rhs)
+{
+  return rhs + n;
+}
+
+template<size_t Ext>
+class extent_type
+{
+public:
+  using index_type = size_t;
+
+  static_assert(Ext >= 0, "A fixed-size Span must be >= 0 in size.");
+
+  constexpr extent_type() {}
+
+  template<index_type Other>
+  MOZ_SPAN_ASSERTION_CONSTEXPR MOZ_IMPLICIT extent_type(extent_type<Other> ext)
+  {
+    static_assert(
+      Other == Ext || Other == dynamic_extent,
+      "Mismatch between fixed-size extent and size of initializing data.");
+    MOZ_RELEASE_ASSERT(ext.size() == Ext);
+  }
+
+  MOZ_SPAN_ASSERTION_CONSTEXPR MOZ_IMPLICIT extent_type(index_type length)
+  {
+    MOZ_RELEASE_ASSERT(length == Ext);
+  }
+
+  constexpr index_type size() const { return Ext; }
+};
+
+template<>
+class extent_type<dynamic_extent>
+{
+public:
+  using index_type = size_t;
+
+  template<index_type Other>
+  explicit constexpr extent_type(extent_type<Other> ext)
+    : size_(ext.size())
+  {
+  }
+
+  explicit constexpr extent_type(index_type length)
+    : size_(length)
+  {
+  }
+
+  constexpr index_type size() const { return size_; }
+
+private:
+  index_type size_;
+};
+} // namespace span_details
+
+/**
+ * Span - slices for C++
+ *
+ * Span implements Rust's slice concept for C++. It's called "Span" instead of
+ * "Slice" to follow the naming used in C++ Core Guidelines.
+ *
+ * A Span wraps a pointer and a length that identify a non-owning view to a
+ * contiguous block of memory of objects of the same type. Various types,
+ * including (pre-decay) C arrays, XPCOM strings, nsTArray, mozilla::Array,
+ * mozilla::Range and contiguous standard-library containers, auto-convert
+ * into Spans when attempting to pass them as arguments to methods that take
+ * Spans. MakeSpan() functions can be used for explicit conversion in other
+ * contexts. (Span itself autoconverts into mozilla::Range.)
+ *
+ * Like Rust's slices, Span provides safety against out-of-bounds access by
+ * performing run-time bound checks. However, unlike Rust's slices, Span
+ * cannot provide safety against use-after-free.
+ *
+ * (Note: Span is like Rust's slice only conceptually. Due to the lack of
+ * ABI guarantees, you should still decompose spans/slices to raw pointer
+ * and length parts when crossing the FFI.)
+ *
+ * In addition to having constructors and MakeSpan() functions that take
+ * various well-known types, a Span for an arbitrary type can be constructed
+ * (via constructor or MakeSpan()) from a pointer and a length or a pointer
+ * and another pointer pointing just past the last element.
+ *
+ * A Span<const char> can be obtained for const char* pointing to a
+ * zero-terminated C string using the MakeCStringSpan() function. A
+ * corresponding implicit constructor does not exist in order to avoid
+ * accidental construction in cases where const char* does not point to a
+ * zero-terminated C string.
+ *
+ * Span has methods that follow the Mozilla naming style and methods that
+ * don't. The methods that follow the Mozilla naming style are meant to be
+ * used directly from Mozilla code. The methods that don't are meant for
+ * integration with C++11 range-based loops and with meta-programming that
+ * expects the same methods that are found on the standard-library
+ * containers. For example, to decompose a Span into its parts in Mozilla
+ * code, use Elements() and Length() (as with nsTArray) instead of data()
+ * and size() (as with std::vector).
+ *
+ * The pointer and length wrapped by a Span cannot be changed after a Span has
+ * been created. When new values are required, simply create a new Span. Span
+ * has a method called Subspan() that works analogously to the Substring()
+ * method of XPCOM strings taking a start index and an optional length. As a
+ * Mozilla extension (relative to Microsoft's gsl::span that mozilla::Span is
+ * based on), Span has methods From(start), To(end) and FromTo(start, end)
+ * that correspond to Rust's &slice[start..], &slice[..end] and
+ * &slice[start..end], respectively. (That is, the end index is the index of
+ * the first element not to be included in the new subspan.)
+ *
+ * When indicating a Span that's only read from, const goes inside the type
+ * parameter. Don't put const in front of Span. That is:
+ * size_t ReadsFromOneSpanAndWritesToAnother(Span<const uint8_t> aReadFrom,
+ *                                           Span<uint8_t> aWrittenTo);
+ *
+ * Any Span<const T> can be viewed as Span<const uint8_t> using the function
+ * AsBytes(). Any Span<T> can be viewed as Span<uint8_t> using the function
+ * AsWritableBytes().
+ */
+template<class ElementType, size_t Extent>
+class Span
+{
+public:
+  // constants and types
+  using element_type = ElementType;
+  using index_type = size_t;
+  using pointer = element_type*;
+  using reference = element_type&;
+
+  using iterator =
+    span_details::span_iterator<Span<ElementType, Extent>, false>;
+  using const_iterator =
+    span_details::span_iterator<Span<ElementType, Extent>, true>;
+  using reverse_iterator = std::reverse_iterator<iterator>;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+  constexpr static const index_type extent = Extent;
+
+  // [Span.cons], Span constructors, copy, assignment, and destructor
+  // "Dependent" is needed to make "span_details::enable_if_t<(Dependent || Extent == 0 || Extent == mozilla::MaxValue<size_t>::value)>" SFINAE,
+  // since "span_details::enable_if_t<(Extent == 0 || Extent == mozilla::MaxValue<size_t>::value)>" is ill-formed when Extent is neither of the extreme values.
+  /**
+   * Constructor with no args.
+   */
+  template<
+    bool Dependent = false,
+    class = span_details::enable_if_t<
+      (Dependent || Extent == 0 || Extent == mozilla::MaxValue<size_t>::value)>>
+  constexpr Span()
+    : storage_(nullptr, span_details::extent_type<0>())
+  {
+  }
+
+  /**
+   * Constructor for nullptr.
+   */
+  constexpr MOZ_IMPLICIT Span(std::nullptr_t) : Span() {}
+
+  /**
+   * Constructor for pointer and length.
+   */
+  constexpr Span(pointer aPtr, index_type aLength)
+    : storage_(aPtr, aLength)
+  {
+  }
+
+  /**
+   * Constructor for start pointer and pointer past end.
+   */
+  constexpr Span(pointer aStartPtr, pointer aEndPtr)
+    : storage_(aStartPtr, std::distance(aStartPtr, aEndPtr))
+  {
+  }
+
+  /**
+   * Constructor for C array.
+   */
+  template<size_t N>
+  constexpr MOZ_IMPLICIT Span(element_type (&aArr)[N])
+    : storage_(&aArr[0], span_details::extent_type<N>())
+  {
+  }
+
+  /**
+   * Constructor for std::array.
+   */
+  template<size_t N,
+           class ArrayElementType = span_details::remove_const_t<element_type>>
+  constexpr MOZ_IMPLICIT Span(std::array<ArrayElementType, N>& aArr)
+    : storage_(&aArr[0], span_details::extent_type<N>())
+  {
+  }
+
+  /**
+   * Constructor for const std::array.
+   */
+  template<size_t N>
+  constexpr MOZ_IMPLICIT Span(
+    const std::array<span_details::remove_const_t<element_type>, N>& aArr)
+    : storage_(&aArr[0], span_details::extent_type<N>())
+  {
+  }
+
+  /**
+   * Constructor for mozilla::Array.
+   */
+  template<size_t N,
+           class ArrayElementType = span_details::remove_const_t<element_type>>
+  constexpr MOZ_IMPLICIT Span(mozilla::Array<ArrayElementType, N>& aArr)
+    : storage_(&aArr[0], span_details::extent_type<N>())
+  {
+  }
+
+  /**
+   * Constructor for const mozilla::Array.
+   */
+  template<size_t N>
+  constexpr MOZ_IMPLICIT Span(
+    const mozilla::Array<span_details::remove_const_t<element_type>, N>& aArr)
+    : storage_(&aArr[0], span_details::extent_type<N>())
+  {
+  }
+
+  /**
+   * Constructor for mozilla::UniquePtr holding an array and length.
+   */
+  template<class ArrayElementType = std::add_pointer<element_type>>
+  constexpr Span(const mozilla::UniquePtr<ArrayElementType>& aPtr,
+                 index_type aLength)
+    : storage_(aPtr.get(), aLength)
+  {
+  }
+
+  // NB: the SFINAE here uses .data() as a incomplete/imperfect proxy for the requirement
+  // on Container to be a contiguous sequence container.
+  /**
+   * Constructor for standard-library containers.
+   */
+  template<
+    class Container,
+    class = span_details::enable_if_t<
+      !span_details::is_span<Container>::value &&
+      !span_details::is_std_array<Container>::value &&
+      mozilla::IsConvertible<typename Container::pointer, pointer>::value &&
+      mozilla::IsConvertible<typename Container::pointer,
+                          decltype(mozilla::DeclVal<Container>().data())>::value>>
+  constexpr MOZ_IMPLICIT Span(Container& cont)
+    : Span(cont.data(), ReleaseAssertedCast<index_type>(cont.size()))
+  {
+  }
+
+  /**
+   * Constructor for standard-library containers (const version).
+   */
+  template<
+    class Container,
+    class = span_details::enable_if_t<
+      mozilla::IsConst<element_type>::value &&
+      !span_details::is_span<Container>::value &&
+      mozilla::IsConvertible<typename Container::pointer, pointer>::value &&
+      mozilla::IsConvertible<typename Container::pointer,
+                          decltype(mozilla::DeclVal<Container>().data())>::value>>
+  constexpr MOZ_IMPLICIT Span(const Container& cont)
+    : Span(cont.data(), ReleaseAssertedCast<index_type>(cont.size()))
+  {
+  }
+
+  /**
+   * Constructor from other Span.
+   */
+  constexpr Span(const Span& other) = default;
+
+  /**
+   * Constructor from other Span.
+   */
+  constexpr Span(Span&& other) = default;
+
+  /**
+   * Constructor from other Span with conversion of element type.
+   */
+  template<
+    class OtherElementType,
+    size_t OtherExtent,
+    class = span_details::enable_if_t<
+      span_details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
+      span_details::is_allowed_element_type_conversion<OtherElementType,
+                                                       element_type>::value>>
+  constexpr MOZ_IMPLICIT Span(const Span<OtherElementType, OtherExtent>& other)
+    : storage_(other.data(),
+               span_details::extent_type<OtherExtent>(other.size()))
+  {
+  }
+
+  /**
+   * Constructor from other Span with conversion of element type.
+   */
+  template<
+    class OtherElementType,
+    size_t OtherExtent,
+    class = span_details::enable_if_t<
+      span_details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
+      span_details::is_allowed_element_type_conversion<OtherElementType,
+                                                       element_type>::value>>
+  constexpr MOZ_IMPLICIT Span(Span<OtherElementType, OtherExtent>&& other)
+    : storage_(other.data(),
+               span_details::extent_type<OtherExtent>(other.size()))
+  {
+  }
+
+  ~Span() = default;
+  MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR Span& operator=(const Span& other)
+    = default;
+
+  MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR Span& operator=(Span&& other)
+    = default;
+
+  // [Span.sub], Span subviews
+  /**
+   * Subspan with first N elements with compile-time N.
+   */
+  template<size_t Count>
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, Count> First() const
+  {
+    MOZ_RELEASE_ASSERT(Count <= size());
+    return { data(), Count };
+  }
+
+  /**
+   * Subspan with last N elements with compile-time N.
+   */
+  template<size_t Count>
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, Count> Last() const
+  {
+    MOZ_RELEASE_ASSERT(Count <= size());
+    return { data() + (size() - Count), Count };
+  }
+
+  /**
+   * Subspan with compile-time start index and length.
+   */
+  template<size_t Offset, size_t Count = dynamic_extent>
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, Count> Subspan() const
+  {
+    MOZ_RELEASE_ASSERT(Offset <= size() &&
+      (Count == dynamic_extent || (Offset + Count <= size())));
+    return { data() + Offset,
+             Count == dynamic_extent ? size() - Offset : Count };
+  }
+
+  /**
+   * Subspan with first N elements with run-time N.
+   */
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> First(
+    index_type aCount) const
+  {
+    MOZ_RELEASE_ASSERT(aCount <= size());
+    return { data(), aCount };
+  }
+
+  /**
+   * Subspan with last N elements with run-time N.
+   */
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> Last(
+    index_type aCount) const
+  {
+    MOZ_RELEASE_ASSERT(aCount <= size());
+    return { data() + (size() - aCount), aCount };
+  }
+
+  /**
+   * Subspan with run-time start index and length.
+   */
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> Subspan(
+    index_type aStart,
+    index_type aLength = dynamic_extent) const
+  {
+    MOZ_RELEASE_ASSERT(aStart <= size() &&
+                       (aLength == dynamic_extent ||
+                        (aStart + aLength <= size())));
+    return { data() + aStart,
+             aLength == dynamic_extent ? size() - aStart : aLength };
+  }
+
+  /**
+   * Subspan with run-time start index. (Rust's &foo[start..])
+   */
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> From(
+    index_type aStart) const
+  {
+    return Subspan(aStart);
+  }
+
+  /**
+   * Subspan with run-time exclusive end index. (Rust's &foo[..end])
+   */
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> To(
+    index_type aEnd) const
+  {
+    return Subspan(0, aEnd);
+  }
+
+  /**
+   * Subspan with run-time start index and exclusive end index.
+   * (Rust's &foo[start..end])
+   */
+  MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> FromTo(
+    index_type aStart,
+    index_type aEnd) const
+  {
+    MOZ_RELEASE_ASSERT(aStart <= aEnd);
+    return Subspan(aStart, aEnd - aStart);
+  }
+
+  // [Span.obs], Span observers
+  /**
+   * Number of elements in the span.
+   */
+  constexpr index_type Length() const { return size(); }
+
+  /**
+   * Number of elements in the span (standard-libray duck typing version).
+   */
+  constexpr index_type size() const { return storage_.size(); }
+
+  /**
+   * Size of the span in bytes.
+   */
+  constexpr index_type LengthBytes() const { return size_bytes(); }
+
+  /**
+   * Size of the span in bytes (standard-library naming style version).
+   */
+  constexpr index_type size_bytes() const
+  {
+    return size() * narrow_cast<index_type>(sizeof(element_type));
+  }
+
+  /**
+   * Checks if the the length of the span is zero.
+   */
+  constexpr bool IsEmpty() const { return empty(); }
+
+  /**
+   * Checks if the the length of the span is zero (standard-libray duck
+   * typing version).
+   */
+  constexpr bool empty() const { return size() == 0; }
+
+  // [Span.elem], Span element access
+  MOZ_SPAN_GCC_CONSTEXPR reference operator[](index_type idx) const
+  {
+    MOZ_RELEASE_ASSERT(idx < storage_.size());
+    return data()[idx];
+  }
+
+  /**
+   * Access element of span by index (standard-library duck typing version).
+   */
+  constexpr reference at(index_type idx) const { return this->operator[](idx); }
+
+  constexpr reference operator()(index_type idx) const
+  {
+    return this->operator[](idx);
+  }
+
+  /**
+   * Pointer to the first element of the span.
+   */
+  constexpr pointer Elements() const { return data(); }
+
+  /**
+   * Pointer to the first element of the span (standard-libray duck typing version).
+   */
+  constexpr pointer data() const { return storage_.data(); }
+
+  // [Span.iter], Span iterator support
+  iterator begin() const { return { this, 0 }; }
+  iterator end() const { return { this, Length() }; }
+
+  const_iterator cbegin() const { return { this, 0 }; }
+  const_iterator cend() const { return { this, Length() }; }
+
+  reverse_iterator rbegin() const
+  {
+    return reverse_iterator{ end() };
+  }
+  reverse_iterator rend() const
+  {
+    return reverse_iterator{ begin() };
+  }
+
+  const_reverse_iterator crbegin() const
+  {
+    return const_reverse_iterator{ cend() };
+  }
+  const_reverse_iterator crend() const
+  {
+    return const_reverse_iterator{ cbegin() };
+  }
+
+private:
+  // this implementation detail class lets us take advantage of the
+  // empty base class optimization to pay for only storage of a single
+  // pointer in the case of fixed-size Spans
+  template<class ExtentType>
+  class storage_type : public ExtentType
+  {
+  public:
+    template<class OtherExtentType>
+    MOZ_SPAN_ASSERTION_CONSTEXPR storage_type(pointer elements,
+                                              OtherExtentType ext)
+      : ExtentType(ext)
+      , data_(elements)
+    {
+      MOZ_RELEASE_ASSERT(
+        (!elements && ExtentType::size() == 0) ||
+        (elements && ExtentType::size() != mozilla::MaxValue<size_t>::value));
+    }
+
+    constexpr pointer data() const { return data_; }
+
+  private:
+    pointer data_;
+  };
+
+  storage_type<span_details::extent_type<Extent>> storage_;
+};
+
+// [Span.comparison], Span comparison operators
+template<class ElementType, size_t FirstExtent, size_t SecondExtent>
+inline constexpr bool
+operator==(const Span<ElementType, FirstExtent>& l,
+           const Span<ElementType, SecondExtent>& r)
+{
+  return (l.size() == r.size()) && std::equal(l.begin(), l.end(), r.begin());
+}
+
+template<class ElementType, size_t Extent>
+inline constexpr bool
+operator!=(const Span<ElementType, Extent>& l,
+           const Span<ElementType, Extent>& r)
+{
+  return !(l == r);
+}
+
+template<class ElementType, size_t Extent>
+inline constexpr bool
+operator<(const Span<ElementType, Extent>& l,
+          const Span<ElementType, Extent>& r)
+{
+  return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template<class ElementType, size_t Extent>
+inline constexpr bool
+operator<=(const Span<ElementType, Extent>& l,
+           const Span<ElementType, Extent>& r)
+{
+  return !(l > r);
+}
+
+template<class ElementType, size_t Extent>
+inline constexpr bool
+operator>(const Span<ElementType, Extent>& l,
+          const Span<ElementType, Extent>& r)
+{
+  return r < l;
+}
+
+template<class ElementType, size_t Extent>
+inline constexpr bool
+operator>=(const Span<ElementType, Extent>& l,
+           const Span<ElementType, Extent>& r)
+{
+  return !(l < r);
+}
+
+namespace span_details {
+// if we only supported compilers with good constexpr support then
+// this pair of classes could collapse down to a constexpr function
+
+// we should use a narrow_cast<> to go to size_t, but older compilers may not see it as
+// constexpr
+// and so will fail compilation of the template
+template<class ElementType, size_t Extent>
+struct calculate_byte_size
+  : mozilla::IntegralConstant<size_t,
+                           static_cast<size_t>(sizeof(ElementType) *
+                                               static_cast<size_t>(Extent))>
+{
+};
+
+template<class ElementType>
+struct calculate_byte_size<ElementType, dynamic_extent>
+  : mozilla::IntegralConstant<size_t, dynamic_extent>
+{
+};
+}
+
+// [Span.objectrep], views of object representation
+/**
+ * View span as Span<const uint8_t>.
+ */
+template<class ElementType, size_t Extent>
+Span<const uint8_t,
+     span_details::calculate_byte_size<ElementType, Extent>::value>
+AsBytes(Span<ElementType, Extent> s)
+{
+  return { reinterpret_cast<const uint8_t*>(s.data()), s.size_bytes() };
+}
+
+/**
+ * View span as Span<uint8_t>.
+ */
+template<class ElementType,
+         size_t Extent,
+         class = span_details::enable_if_t<!mozilla::IsConst<ElementType>::value>>
+Span<uint8_t, span_details::calculate_byte_size<ElementType, Extent>::value>
+AsWritableBytes(Span<ElementType, Extent> s)
+{
+  return { reinterpret_cast<uint8_t*>(s.data()), s.size_bytes() };
+}
+
+//
+// MakeSpan() - Utility functions for creating Spans
+//
+/**
+ * Create span from pointer and length.
+ */
+template<class ElementType>
+Span<ElementType>
+MakeSpan(ElementType* aPtr, typename Span<ElementType>::index_type aLength)
+{
+  return Span<ElementType>(aPtr, aLength);
+}
+
+/**
+ * Create span from start pointer and pointer past end.
+ */
+template<class ElementType>
+Span<ElementType>
+MakeSpan(ElementType* aStartPtr, ElementType* aEndPtr)
+{
+  return Span<ElementType>(aStartPtr, aEndPtr);
+}
+
+/**
+ * Create span from C array.
+ */
+template<class ElementType, size_t N>
+Span<ElementType> MakeSpan(ElementType (&aArr)[N])
+{
+  return Span<ElementType>(aArr);
+}
+
+/**
+ * Create span from mozilla::Array.
+ */
+template<class ElementType, size_t N>
+Span<ElementType>
+MakeSpan(mozilla::Array<ElementType, N>& aArr)
+{
+  return aArr;
+}
+
+/**
+ * Create span from const mozilla::Array.
+ */
+template<class ElementType, size_t N>
+Span<const ElementType>
+MakeSpan(const mozilla::Array<ElementType, N>& arr)
+{
+  return arr;
+}
+
+/**
+ * Create span from standard-library container.
+ */
+template<class Container>
+Span<typename Container::value_type>
+MakeSpan(Container& cont)
+{
+  return Span<typename Container::value_type>(cont);
+}
+
+/**
+ * Create span from standard-library container (const version).
+ */
+template<class Container>
+Span<const typename Container::value_type>
+MakeSpan(const Container& cont)
+{
+  return Span<const typename Container::value_type>(cont);
+}
+
+/**
+ * Create span from smart pointer and length.
+ */
+template<class Ptr>
+Span<typename Ptr::element_type>
+MakeSpan(Ptr& aPtr, size_t aLength)
+{
+  return Span<typename Ptr::element_type>(aPtr, aLength);
+}
+
+/**
+ * Create span from C string.
+ */
+inline Span<const char>
+MakeCStringSpan(const char* aStr)
+{
+  return Span<const char>(aStr, std::strlen(aStr));
+}
+
+} // namespace mozilla
+
+#ifdef _MSC_VER
+#if _MSC_VER < 1910
+#undef constexpr
+#pragma pop_macro("constexpr")
+
+#endif // _MSC_VER < 1910
+
+#pragma warning(pop)
+#endif // _MSC_VER
+
+#undef MOZ_SPAN_ASSERTION_CONSTEXPR
+#undef MOZ_SPAN_GCC_CONSTEXPR
+#undef MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR
+#undef MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN
+#undef MOZ_SPAN_NON_CONST_CONSTEXPR
+
+#endif // mozilla_Span_h
diff --git a/mfbt/moz.build b/mfbt/moz.build
index 897a686f4..ea3c3b701 100644
--- a/mfbt/moz.build
+++ b/mfbt/moz.build
@@ -82,6 +82,7 @@ EXPORTS.mozilla = [
     'SegmentedVector.h',
     'SHA1.h',
     'SizePrintfMacros.h',
+    'Span.h',
     'SplayTree.h',
     'Sprintf.h',
     'StaticAnalysisFunctions.h',
diff --git a/mfbt/tests/gtest/TestSpan.cpp b/mfbt/tests/gtest/TestSpan.cpp
new file mode 100644
index 000000000..f3aa000a4
--- /dev/null
+++ b/mfbt/tests/gtest/TestSpan.cpp
@@ -0,0 +1,2079 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+// Adapted from https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/tests/Span_tests.cpp
+
+#include "gtest/gtest.h"
+
+#include "mozilla/Span.h"
+
+#include "nsString.h"
+#include "nsTArray.h"
+#include "mozilla/Range.h"
+#include "mozilla/TypeTraits.h"
+
+#define SPAN_TEST(name) TEST(SpanTest, name)
+#define CHECK_THROW(a, b)
+
+using namespace std;
+using namespace mozilla;
+
+static_assert(IsConvertible<Range<int>, Span<const int>>::value,
+              "Range should convert into const");
+static_assert(IsConvertible<Range<const int>, Span<const int>>::value,
+              "const Range should convert into const");
+static_assert(!IsConvertible<Range<const int>, Span<int>>::value,
+              "Range should not drop const in conversion");
+static_assert(IsConvertible<Span<int>, Range<const int>>::value,
+              "Span should convert into const");
+static_assert(IsConvertible<Span<const int>, Range<const int>>::value,
+              "const Span should convert into const");
+static_assert(!IsConvertible<Span<const int>, Range<int>>::value,
+              "Span should not drop const in conversion");
+static_assert(IsConvertible<Span<const int>, Span<const int>>::value,
+              "const Span should convert into const");
+static_assert(IsConvertible<Span<int>, Span<const int>>::value,
+              "Span should convert into const");
+static_assert(!IsConvertible<Span<const int>, Span<int>>::value,
+              "Span should not drop const in conversion");
+static_assert(IsConvertible<const nsTArray<int>, Span<const int>>::value,
+              "const nsTArray should convert into const");
+static_assert(IsConvertible<nsTArray<int>, Span<const int>>::value,
+              "nsTArray should convert into const");
+static_assert(!IsConvertible<const nsTArray<int>, Span<int>>::value,
+              "nsTArray should not drop const in conversion");
+static_assert(IsConvertible<nsTArray<const int>, Span<const int>>::value,
+              "nsTArray should convert into const");
+static_assert(!IsConvertible<nsTArray<const int>, Span<int>>::value,
+              "nsTArray should not drop const in conversion");
+
+namespace {
+struct BaseClass
+{
+};
+struct DerivedClass : BaseClass
+{
+};
+}
+
+void
+AssertSpanOfThreeInts(Span<const int> s)
+{
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 1);
+  ASSERT_EQ(s[1], 2);
+  ASSERT_EQ(s[2], 3);
+}
+
+void
+AssertSpanOfThreeChars(Span<const char> s)
+{
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 'a');
+  ASSERT_EQ(s[1], 'b');
+  ASSERT_EQ(s[2], 'c');
+}
+
+void
+AssertSpanOfThreeChar16s(Span<const char16_t> s)
+{
+  ASSERT_EQ(s.size(), 3U);
+  ASSERT_EQ(s[0], 'a');
+  ASSERT_EQ(s[1], 'b');
+  ASSERT_EQ(s[2], 'c');
+}
+
+void
+AssertSpanOfThreeCharsViaString(const nsACString& aStr)
+{
+  AssertSpanOfThreeChars(aStr);
+}
+
+void
+AssertSpanOfThreeChar16sViaString(const nsAString& aStr)
+{
+  AssertSpanOfThreeChar16s(aStr);
+}
+
+SPAN_TEST(default_constructor)
+{
+  {
+    Span<int> s;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int> cs;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+  {
+    Span<int, 0> s;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int, 0> cs;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<int, 1> s;
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), nullptr); // explains why it can't compile
+#endif
+  }
+
+  {
+    Span<int> s{};
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int> cs{};
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+}
+
+SPAN_TEST(size_optimization)
+{
+  {
+    Span<int> s;
+    ASSERT_EQ(sizeof(s), sizeof(int*) + sizeof(size_t));
+  }
+
+  {
+    Span<int, 0> s;
+    ASSERT_EQ(sizeof(s), sizeof(int*));
+  }
+}
+
+SPAN_TEST(from_nullptr_constructor)
+{
+  {
+    Span<int> s = nullptr;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int> cs = nullptr;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+  {
+    Span<int, 0> s = nullptr;
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int, 0> cs = nullptr;
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<int, 1> s = nullptr;
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), nullptr); // explains why it can't compile
+#endif
+  }
+
+  {
+    Span<int> s{ nullptr };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int> cs{ nullptr };
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+  {
+    Span<int*> s{ nullptr };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int*> cs{ nullptr };
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+}
+
+SPAN_TEST(from_nullptr_length_constructor)
+{
+  {
+    Span<int> s{ nullptr, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int> cs{ nullptr, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+  {
+    Span<int, 0> s{ nullptr, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int, 0> cs{ nullptr, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+
+#if 0
+        {
+            auto workaround_macro = []() { Span<int, 1> s{ nullptr, static_cast<Span<int>::index_type>(0) }; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { Span<int> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { Span<const int> cs{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { Span<int, 0> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { Span<const int, 0> s{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+#endif
+  {
+    Span<int*> s{ nullptr, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+
+    Span<const int*> cs{ nullptr, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(cs.Length(), 0U);
+    ASSERT_EQ(cs.data(), nullptr);
+  }
+}
+
+SPAN_TEST(from_pointer_length_constructor)
+{
+  int arr[4] = { 1, 2, 3, 4 };
+
+  {
+    Span<int> s{ &arr[0], 2 };
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int, 2> s{ &arr[0], 2 };
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    int* p = nullptr;
+    Span<int> s{ p, static_cast<Span<int>::index_type>(0) };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+  }
+
+#if 0
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { Span<int> s{p, 2}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+#endif
+
+  {
+    auto s = MakeSpan(&arr[0], 2);
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    int* p = nullptr;
+    auto s = MakeSpan(p, static_cast<Span<int>::index_type>(0));
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+  }
+
+#if 0
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { MakeSpan(p, 2); };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+#endif
+}
+
+SPAN_TEST(from_pointer_pointer_constructor)
+{
+  int arr[4] = { 1, 2, 3, 4 };
+
+  {
+    Span<int> s{ &arr[0], &arr[2] };
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int, 2> s{ &arr[0], &arr[2] };
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    Span<int> s{ &arr[0], &arr[0] };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 0> s{ &arr[0], &arr[0] };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  // this will fail the std::distance() precondition, which asserts on MSVC debug builds
+  //{
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[1], &arr[0]}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  // this will fail the std::distance() precondition, which asserts on MSVC debug builds
+  //{
+  //    int* p = nullptr;
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[0], p}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  {
+    int* p = nullptr;
+    Span<int> s{ p, p };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+  }
+
+  {
+    int* p = nullptr;
+    Span<int, 0> s{ p, p };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+  }
+
+  // this will fail the std::distance() precondition, which asserts on MSVC debug builds
+  //{
+  //    int* p = nullptr;
+  //    auto workaround_macro = [&]() { Span<int> s{&arr[0], p}; };
+  //    CHECK_THROW(workaround_macro(), fail_fast);
+  //}
+
+  {
+    auto s = MakeSpan(&arr[0], &arr[2]);
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[1], 2);
+  }
+
+  {
+    auto s = MakeSpan(&arr[0], &arr[0]);
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    int* p = nullptr;
+    auto s = MakeSpan(p, p);
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), nullptr);
+  }
+}
+
+SPAN_TEST(from_array_constructor)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+
+  {
+    Span<int> s{ arr };
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 5> s{ arr };
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  int arr2d[2][3] = { { 1, 2, 3 }, { 4, 5, 6 } };
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 6> s{ arr };
+  }
+
+  {
+    Span<int, 0> s{ arr };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<int> s{ arr2d };
+    ASSERT_EQ(s.Length(), 6U);
+    ASSERT_EQ(s.data(), &arr2d[0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[5], 6);
+  }
+
+  {
+    Span<int, 0> s{ arr2d };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr2d[0][0]);
+  }
+
+  {
+    Span<int, 6> s{ arr2d };
+  }
+#endif
+  {
+    Span<int[3]> s{ &(arr2d[0]), 1 };
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr2d[0]);
+  }
+
+  int arr3d[2][3][2] = { { { 1, 2 }, { 3, 4 }, { 5, 6 } },
+                         { { 7, 8 }, { 9, 10 }, { 11, 12 } } };
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int> s{ arr3d };
+    ASSERT_EQ(s.Length(), 12U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[11], 12);
+  }
+
+  {
+    Span<int, 0> s{ arr3d };
+    ASSERT_EQ(s.Length(), 0U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+  }
+
+  {
+    Span<int, 11> s{ arr3d };
+  }
+
+  {
+    Span<int, 12> s{ arr3d };
+    ASSERT_EQ(s.Length(), 12U);
+    ASSERT_EQ(s.data(), &arr3d[0][0][0]);
+    ASSERT_EQ(s[0], 1);
+    ASSERT_EQ(s[5], 6);
+  }
+#endif
+  {
+    Span<int[3][2]> s{ &arr3d[0], 1 };
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr3d[0]);
+  }
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.Length(), 5U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    auto s = MakeSpan(&(arr2d[0]), 1);
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr2d[0]);
+  }
+
+  {
+    auto s = MakeSpan(&arr3d[0], 1);
+    ASSERT_EQ(s.Length(), 1U);
+    ASSERT_EQ(s.data(), &arr3d[0]);
+  }
+}
+
+SPAN_TEST(from_dynamic_array_constructor)
+{
+  double(*arr)[3][4] = new double[100][3][4];
+
+  {
+    Span<double> s(&arr[0][0][0], 10);
+    ASSERT_EQ(s.Length(), 10U);
+    ASSERT_EQ(s.data(), &arr[0][0][0]);
+  }
+
+  {
+    auto s = MakeSpan(&arr[0][0][0], 10);
+    ASSERT_EQ(s.Length(), 10U);
+    ASSERT_EQ(s.data(), &arr[0][0][0]);
+  }
+
+  delete[] arr;
+}
+
+SPAN_TEST(from_std_array_constructor)
+{
+  std::array<int, 4> arr = { { 1, 2, 3, 4 } };
+
+  {
+    Span<int> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int> cs{ arr };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 4> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 4> cs{ arr };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s{ arr };
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 2> cs{ arr };
+    ASSERT_EQ(cs.size(), 2U);
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 0> s{ arr };
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+
+    Span<const int, 0> cs{ arr };
+    ASSERT_EQ(cs.size(), 0U);
+    ASSERT_EQ(cs.data(), arr.data());
+  }
+
+  {
+    Span<int, 5> s{ arr };
+  }
+
+  {
+    auto get_an_array = []() -> std::array<int, 4> { return { 1, 2, 3, 4 }; };
+    auto take_a_Span = [](Span<int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> std::array<int, 4> {
+      return { { 1, 2, 3, 4 } };
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_const_std_array_constructor)
+{
+  const std::array<int, 4> arr = { { 1, 2, 3, 4 } };
+
+  {
+    Span<const int> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 4> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{ arr };
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 0> s{ arr };
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 5> s{ arr };
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> const std::array<int, 4> {
+      return { { 1, 2, 3, 4 } };
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary std::array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_std_array_const_constructor)
+{
+  std::array<const int, 4> arr = { { 1, 2, 3, 4 } };
+
+  {
+    Span<const int> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 4> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{ arr };
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 0> s{ arr };
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), arr.data());
+  }
+
+  {
+    Span<const int, 5> s{ arr };
+  }
+
+  {
+    Span<int, 4> s{ arr };
+  }
+#endif
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.size()));
+    ASSERT_EQ(s.data(), arr.data());
+  }
+}
+
+SPAN_TEST(from_mozilla_array_constructor)
+{
+  mozilla::Array<int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<int> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int> cs{ arr };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 4> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 4> cs{ arr };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s{ arr };
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 2> cs{ arr };
+    ASSERT_EQ(cs.size(), 2U);
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 0> s{ arr };
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+
+    Span<const int, 0> cs{ arr };
+    ASSERT_EQ(cs.size(), 0U);
+    ASSERT_EQ(cs.data(), &arr[0]);
+  }
+
+  {
+    Span<int, 5> s{ arr };
+  }
+
+  {
+    auto get_an_array = []() -> mozilla::Array<int, 4> {
+      return { 1, 2, 3, 4 };
+    };
+    auto take_a_Span = [](Span<int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto get_an_array = []() -> mozilla::Array<int, 4> {
+      return { 1, 2, 3, 4 };
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_const_mozilla_array_constructor)
+{
+  const mozilla::Array<int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<const int> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 4> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{ arr };
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 0> s{ arr };
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 5> s{ arr };
+  }
+#endif
+
+#if 0
+  {
+    auto get_an_array = []() -> const mozilla::Array<int, 4> {
+      return { 1, 2, 3, 4 };
+    };
+    auto take_a_Span = [](Span<const int> s) { static_cast<void>(s); };
+    // try to take a temporary mozilla::Array
+    take_a_Span(get_an_array());
+  }
+#endif
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_mozilla_array_const_constructor)
+{
+  mozilla::Array<const int, 4> arr(1, 2, 3, 4);
+
+  {
+    Span<const int> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 4> s{ arr };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<const int, 2> s{ arr };
+    ASSERT_EQ(s.size(), 2U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 0> s{ arr };
+    ASSERT_EQ(s.size(), 0U);
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+
+  {
+    Span<const int, 5> s{ arr };
+  }
+
+  {
+    Span<int, 4> s{ arr };
+  }
+#endif
+
+  {
+    auto s = MakeSpan(arr);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(arr.cend() - arr.cbegin()));
+    ASSERT_EQ(s.data(), &arr[0]);
+  }
+}
+
+SPAN_TEST(from_container_constructor)
+{
+  std::vector<int> v = { 1, 2, 3 };
+  const std::vector<int> cv = v;
+
+  {
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{ v };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(s.data(), v.data());
+
+    Span<const int> cs{ v };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(cs.data(), v.data());
+  }
+
+  std::string str = "hello";
+  const std::string cstr = "hello";
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> s{ str };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.size()));
+    ASSERT_EQ(s.data(), str.data());
+#endif
+    Span<const char> cs{ str };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.size()));
+    ASSERT_EQ(cs.data(), str.data());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    Span<char> s{ cstr };
+#endif
+    Span<const char> cs{ cstr };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(cstr.size()));
+    ASSERT_EQ(cs.data(), cstr.data());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_vector = []() -> std::vector<int> { return {}; };
+    auto use_Span = [](Span<int> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+#endif
+  }
+
+  {
+    auto get_temp_vector = []() -> std::vector<int> { return {}; };
+    auto use_Span = [](Span<const int> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_string = []() -> std::string { return {}; };
+    auto use_Span = [](Span<char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+#endif
+  }
+
+  {
+    auto get_temp_string = []() -> std::string { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    auto get_temp_vector = []() -> const std::vector<int> { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_vector());
+#endif
+  }
+
+  {
+    auto get_temp_string = []() -> const std::string { return {}; };
+    auto use_Span = [](Span<const char> s) { static_cast<void>(s); };
+    use_Span(get_temp_string());
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    std::map<int, int> m;
+    Span<int> s{ m };
+#endif
+  }
+
+  {
+    auto s = MakeSpan(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.size()));
+    ASSERT_EQ(s.data(), v.data());
+
+    auto cs = MakeSpan(cv);
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(cv.size()));
+    ASSERT_EQ(cs.data(), cv.data());
+  }
+}
+
+SPAN_TEST(from_xpcom_collections)
+{
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{ v };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{ v };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = MakeSpan(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    AutoTArray<int, 5> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{ v };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{ v };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    AutoTArray<int, 5> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = MakeSpan(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    FallibleTArray<int> v;
+    *(v.AppendElement(fallible)) = 1;
+    *(v.AppendElement(fallible)) = 2;
+    *(v.AppendElement(fallible)) = 3;
+
+    AssertSpanOfThreeInts(v);
+
+    Span<int> s{ v };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{ v };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    FallibleTArray<int> v;
+    *(v.AppendElement(fallible)) = 1;
+    *(v.AppendElement(fallible)) = 2;
+    *(v.AppendElement(fallible)) = 3;
+
+    AssertSpanOfThreeInts(v);
+
+    auto s = MakeSpan(v);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+  {
+    nsAutoString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChar16s(str);
+    AssertSpanOfThreeChar16sViaString(str);
+
+    Span<char16_t> s{ str };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginWriting());
+    ASSERT_EQ(s[2], 'c');
+
+    Span<const char16_t> cs{ str };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(cs.data(), str.BeginReading());
+    ASSERT_EQ(cs[2], 'c');
+  }
+  {
+    nsAutoString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChar16s(str);
+    AssertSpanOfThreeChar16sViaString(str);
+
+    auto s = MakeSpan(str);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginWriting());
+    ASSERT_EQ(s[2], 'c');
+  }
+  {
+    nsAutoCString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChars(str);
+    AssertSpanOfThreeCharsViaString(str);
+
+    Span<uint8_t> s{ str };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), reinterpret_cast<uint8_t*>(str.BeginWriting()));
+    ASSERT_EQ(s[2], 'c');
+
+    Span<const uint8_t> cs{ str };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(cs.data(), reinterpret_cast<const uint8_t*>(str.BeginReading()));
+    ASSERT_EQ(cs[2], 'c');
+  }
+  {
+    nsAutoCString str;
+    str.AssignLiteral("abc");
+
+    AssertSpanOfThreeChars(str);
+    AssertSpanOfThreeCharsViaString(str);
+
+    auto s = MakeSpan(str);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(str.Length()));
+    ASSERT_EQ(s.data(), str.BeginWriting());
+    ASSERT_EQ(s[2], 'c');
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    Range<int> r(v.Elements(), v.Length());
+
+    AssertSpanOfThreeInts(r);
+
+    Span<int> s{ r };
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+
+    Span<const int> cs{ r };
+    ASSERT_EQ(cs.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(cs.data(), v.Elements());
+    ASSERT_EQ(cs[2], 3);
+  }
+  {
+    nsTArray<int> v;
+    v.AppendElement(1);
+    v.AppendElement(2);
+    v.AppendElement(3);
+
+    Range<int> r(v.Elements(), v.Length());
+
+    AssertSpanOfThreeInts(r);
+
+    auto s = MakeSpan(r);
+    ASSERT_EQ(s.size(), narrow_cast<size_t>(v.Length()));
+    ASSERT_EQ(s.data(), v.Elements());
+    ASSERT_EQ(s[2], 3);
+  }
+}
+
+SPAN_TEST(from_cstring)
+{
+  {
+    const char* str = "abc";
+
+    auto cs = MakeCStringSpan(str);
+    ASSERT_EQ(cs.size(), 3U);
+    ASSERT_EQ(cs.data(), str);
+    ASSERT_EQ(cs[2], 'c');
+  }
+}
+
+SPAN_TEST(from_convertible_Span_constructor){
+  {
+    Span<DerivedClass> avd;
+    Span<const DerivedClass> avcd = avd;
+    static_cast<void>(avcd);
+  }
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+  Span<DerivedClass> avd;
+  Span<BaseClass> avb = avd;
+  static_cast<void>(avb);
+#endif
+  }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int> s;
+    Span<unsigned int> s2 = s;
+    static_cast<void>(s2);
+  }
+
+  {
+    Span<int> s;
+    Span<const unsigned int> s2 = s;
+    static_cast<void>(s2);
+  }
+
+  {
+    Span<int> s;
+    Span<short> s2 = s;
+    static_cast<void>(s2);
+  }
+#endif
+}
+
+SPAN_TEST(copy_move_and_assignment)
+{
+  Span<int> s1;
+  ASSERT_TRUE(s1.empty());
+
+  int arr[] = { 3, 4, 5 };
+
+  Span<const int> s2 = arr;
+  ASSERT_EQ(s2.Length(), 3U);
+  ASSERT_EQ(s2.data(), &arr[0]);
+
+  s2 = s1;
+  ASSERT_TRUE(s2.empty());
+
+  auto get_temp_Span = [&]() -> Span<int> { return { &arr[1], 2 }; };
+  auto use_Span = [&](Span<const int> s) {
+    ASSERT_EQ(s.Length(), 2U);
+    ASSERT_EQ(s.data(), &arr[1]);
+  };
+  use_Span(get_temp_Span());
+
+  s1 = get_temp_Span();
+  ASSERT_EQ(s1.Length(), 2U);
+  ASSERT_EQ(s1.data(), &arr[1]);
+}
+
+SPAN_TEST(first)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<2>().Length(), 2U);
+    ASSERT_EQ(av.First(2).Length(), 2U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<0>().Length(), 0U);
+    ASSERT_EQ(av.First(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.First<5>().Length(), 5U);
+    ASSERT_EQ(av.First(5).Length(), 5U);
+  }
+
+#if 0
+        {
+            Span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+            ASSERT_EQ(av.First<6>().Length() , 6U);
+            ASSERT_EQ(av.First<-1>().Length() , -1);
+#endif
+            CHECK_THROW(av.First(6).Length(), fail_fast);
+        }
+#endif
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.First<0>().Length(), 0U);
+    ASSERT_EQ(av.First(0).Length(), 0U);
+  }
+}
+
+SPAN_TEST(last)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<2>().Length(), 2U);
+    ASSERT_EQ(av.Last(2).Length(), 2U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<0>().Length(), 0U);
+    ASSERT_EQ(av.Last(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Last<5>().Length(), 5U);
+    ASSERT_EQ(av.Last(5).Length(), 5U);
+  }
+
+#if 0
+        {
+            Span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+            ASSERT_EQ(av.Last<6>().Length() , 6U);
+#endif
+            CHECK_THROW(av.Last(6).Length(), fail_fast);
+        }
+#endif
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.Last<0>().Length(), 0U);
+    ASSERT_EQ(av.Last(0).Length(), 0U);
+  }
+}
+
+SPAN_TEST(from_to)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(3).Length(), 2U);
+    ASSERT_EQ(av.From(2)[1], 4);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(5).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.From(0).Length(), 5U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(3).Length(), 3U);
+    ASSERT_EQ(av.To(3)[1], 2);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.To(5).Length(), 5U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(1, 4).Length(), 3U);
+    ASSERT_EQ(av.FromTo(1, 4)[1], 3);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(2, 2).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.FromTo(0, 5).Length(), 5U);
+  }
+}
+
+SPAN_TEST(Subspan)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<2, 2>().Length()), 2U);
+    ASSERT_EQ(av.Subspan(2, 2).Length(), 2U);
+    ASSERT_EQ(av.Subspan(2, 3).Length(), 3U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<0, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(0, 0).Length(), 0U);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<0, 5>().Length()), 5U);
+    ASSERT_EQ(av.Subspan(0, 5).Length(), 5U);
+    CHECK_THROW(av.Subspan(0, 6).Length(), fail_fast);
+    CHECK_THROW(av.Subspan(1, 5).Length(), fail_fast);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ((av.Subspan<4, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(4, 0).Length(), 0U);
+    ASSERT_EQ(av.Subspan(5, 0).Length(), 0U);
+    CHECK_THROW(av.Subspan(6, 0).Length(), fail_fast);
+  }
+
+  {
+    Span<int> av;
+    ASSERT_EQ((av.Subspan<0, 0>().Length()), 0U);
+    ASSERT_EQ(av.Subspan(0, 0).Length(), 0U);
+    CHECK_THROW((av.Subspan<1, 0>().Length()), fail_fast);
+  }
+
+  {
+    Span<int> av;
+    ASSERT_EQ(av.Subspan(0).Length(), 0U);
+    CHECK_THROW(av.Subspan(1).Length(), fail_fast);
+  }
+
+  {
+    Span<int> av = arr;
+    ASSERT_EQ(av.Subspan(0).Length(), 5U);
+    ASSERT_EQ(av.Subspan(1).Length(), 4U);
+    ASSERT_EQ(av.Subspan(4).Length(), 1U);
+    ASSERT_EQ(av.Subspan(5).Length(), 0U);
+    CHECK_THROW(av.Subspan(6).Length(), fail_fast);
+    auto av2 = av.Subspan(1);
+    for (int i = 0; i < 4; ++i)
+      ASSERT_EQ(av2[i], i + 2);
+  }
+
+  {
+    Span<int, 5> av = arr;
+    ASSERT_EQ(av.Subspan(0).Length(), 5U);
+    ASSERT_EQ(av.Subspan(1).Length(), 4U);
+    ASSERT_EQ(av.Subspan(4).Length(), 1U);
+    ASSERT_EQ(av.Subspan(5).Length(), 0U);
+    CHECK_THROW(av.Subspan(6).Length(), fail_fast);
+    auto av2 = av.Subspan(1);
+    for (int i = 0; i < 4; ++i)
+      ASSERT_EQ(av2[i], i + 2);
+  }
+}
+
+SPAN_TEST(at_call)
+{
+  int arr[4] = { 1, 2, 3, 4 };
+
+  {
+    Span<int> s = arr;
+    ASSERT_EQ(s.at(0), 1);
+    CHECK_THROW(s.at(5), fail_fast);
+  }
+
+  {
+    int arr2d[2] = { 1, 6 };
+    Span<int, 2> s = arr2d;
+    ASSERT_EQ(s.at(0), 1);
+    ASSERT_EQ(s.at(1), 6);
+    CHECK_THROW(s.at(2), fail_fast);
+  }
+}
+
+SPAN_TEST(operator_function_call)
+{
+  int arr[4] = { 1, 2, 3, 4 };
+
+  {
+    Span<int> s = arr;
+    ASSERT_EQ(s(0), 1);
+    CHECK_THROW(s(5), fail_fast);
+  }
+
+  {
+    int arr2d[2] = { 1, 6 };
+    Span<int, 2> s = arr2d;
+    ASSERT_EQ(s(0), 1);
+    ASSERT_EQ(s(1), 6);
+    CHECK_THROW(s(2), fail_fast);
+  }
+}
+
+SPAN_TEST(iterator_default_init)
+{
+  Span<int>::iterator it1;
+  Span<int>::iterator it2;
+  ASSERT_EQ(it1, it2);
+}
+
+SPAN_TEST(const_iterator_default_init)
+{
+  Span<int>::const_iterator it1;
+  Span<int>::const_iterator it2;
+  ASSERT_EQ(it1, it2);
+}
+
+SPAN_TEST(iterator_conversions)
+{
+  Span<int>::iterator badIt;
+  Span<int>::const_iterator badConstIt;
+  ASSERT_EQ(badIt, badConstIt);
+
+  int a[] = { 1, 2, 3, 4 };
+  Span<int> s = a;
+
+  auto it = s.begin();
+  auto cit = s.cbegin();
+
+  ASSERT_EQ(it, cit);
+  ASSERT_EQ(cit, it);
+
+  Span<int>::const_iterator cit2 = it;
+  ASSERT_EQ(cit2, cit);
+
+  Span<int>::const_iterator cit3 = it + 4;
+  ASSERT_EQ(cit3, s.cend());
+}
+
+SPAN_TEST(iterator_comparisons)
+{
+  int a[] = { 1, 2, 3, 4 };
+  {
+    Span<int> s = a;
+    Span<int>::iterator it = s.begin();
+    auto it2 = it + 1;
+    Span<int>::const_iterator cit = s.cbegin();
+
+    ASSERT_EQ(it, cit);
+    ASSERT_EQ(cit, it);
+    ASSERT_EQ(it, it);
+    ASSERT_EQ(cit, cit);
+    ASSERT_EQ(cit, s.begin());
+    ASSERT_EQ(s.begin(), cit);
+    ASSERT_EQ(s.cbegin(), cit);
+    ASSERT_EQ(it, s.begin());
+    ASSERT_EQ(s.begin(), it);
+
+    ASSERT_NE(it, it2);
+    ASSERT_NE(it2, it);
+    ASSERT_NE(it, s.end());
+    ASSERT_NE(it2, s.end());
+    ASSERT_NE(s.end(), it);
+    ASSERT_NE(it2, cit);
+    ASSERT_NE(cit, it2);
+
+    ASSERT_LT(it, it2);
+    ASSERT_LE(it, it2);
+    ASSERT_LE(it2, s.end());
+    ASSERT_LT(it, s.end());
+    ASSERT_LE(it, cit);
+    ASSERT_LE(cit, it);
+    ASSERT_LT(cit, it2);
+    ASSERT_LE(cit, it2);
+    ASSERT_LT(cit, s.end());
+    ASSERT_LE(cit, s.end());
+
+    ASSERT_GT(it2, it);
+    ASSERT_GE(it2, it);
+    ASSERT_GT(s.end(), it2);
+    ASSERT_GE(s.end(), it2);
+    ASSERT_GT(it2, cit);
+    ASSERT_GE(it2, cit);
+  }
+}
+
+SPAN_TEST(begin_end)
+{
+  {
+    int a[] = { 1, 2, 3, 4 };
+    Span<int> s = a;
+
+    Span<int>::iterator it = s.begin();
+    Span<int>::iterator it2 = std::begin(s);
+    ASSERT_EQ(it, it2);
+
+    it = s.end();
+    it2 = std::end(s);
+    ASSERT_EQ(it, it2);
+  }
+
+  {
+    int a[] = { 1, 2, 3, 4 };
+    Span<int> s = a;
+
+    auto it = s.begin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 1);
+
+    auto beyond = s.end();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 2);
+    *it = 22;
+    ASSERT_EQ(*it, 22);
+    ASSERT_EQ(beyond - it, 3U);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.end()) {
+      *it = 5;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+
+    for (auto& n : s) {
+      ASSERT_EQ(n, 5);
+    }
+  }
+}
+
+SPAN_TEST(cbegin_cend)
+{
+#if 0
+          {
+              int a[] = { 1, 2, 3, 4 };
+              Span<int> s = a;
+
+              Span<int>::const_iterator cit = s.cbegin();
+              Span<int>::const_iterator cit2 = std::cbegin(s);
+              ASSERT_EQ(cit , cit2);
+
+              cit = s.cend();
+              cit2 = std::cend(s);
+              ASSERT_EQ(cit , cit2);
+          }
+#endif
+  {
+    int a[] = { 1, 2, 3, 4 };
+    Span<int> s = a;
+
+    auto it = s.cbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 1);
+
+    auto beyond = s.cend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 2);
+    ASSERT_EQ(beyond - it, 3U);
+
+    int last = 0;
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.cend()) {
+      ASSERT_EQ(*it, last + 1);
+
+      last = *it;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+  }
+}
+
+SPAN_TEST(rbegin_rend)
+{
+  {
+    int a[] = { 1, 2, 3, 4 };
+    Span<int> s = a;
+
+    auto it = s.rbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 4);
+
+    auto beyond = s.rend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 3);
+    *it = 22;
+    ASSERT_EQ(*it, 22);
+    ASSERT_EQ(beyond - it, 3U);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    while (it != s.rend()) {
+      *it = 5;
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+
+    for (auto& n : s) {
+      ASSERT_EQ(n, 5);
+    }
+  }
+}
+
+SPAN_TEST(crbegin_crend)
+{
+  {
+    int a[] = { 1, 2, 3, 4 };
+    Span<int> s = a;
+
+    auto it = s.crbegin();
+    auto first = it;
+    ASSERT_EQ(it, first);
+    ASSERT_EQ(*it, 4);
+
+    auto beyond = s.crend();
+    ASSERT_NE(it, beyond);
+    CHECK_THROW(*beyond, fail_fast);
+
+    ASSERT_EQ(beyond - first, 4U);
+    ASSERT_EQ(first - first, 0U);
+    ASSERT_EQ(beyond - beyond, 0U);
+
+    ++it;
+    ASSERT_EQ(it - first, 1U);
+    ASSERT_EQ(*it, 3);
+    ASSERT_EQ(beyond - it, 3U);
+
+    it = first;
+    ASSERT_EQ(it, first);
+    int last = 5;
+    while (it != s.crend()) {
+      ASSERT_EQ(*it, last - 1);
+      last = *it;
+
+      ++it;
+    }
+
+    ASSERT_EQ(it, beyond);
+    ASSERT_EQ(it - beyond, 0U);
+  }
+}
+
+SPAN_TEST(comparison_operators)
+{
+  {
+    Span<int> s1 = nullptr;
+    Span<int> s2 = nullptr;
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = { 2, 1 };
+    Span<int> s1 = arr;
+    Span<int> s2 = arr;
+
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = { 2, 1 }; // bigger
+
+    Span<int> s1 = nullptr;
+    Span<int> s2 = arr;
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+
+  {
+    int arr1[] = { 1, 2 };
+    int arr2[] = { 1, 2 };
+    Span<int> s1 = arr1;
+    Span<int> s2 = arr2;
+
+    ASSERT_EQ(s1, s2);
+    ASSERT_FALSE(s1 != s2);
+    ASSERT_FALSE(s1 < s2);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s1, s2);
+    ASSERT_EQ(s2, s1);
+    ASSERT_FALSE(s2 != s1);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s2, s1);
+    ASSERT_FALSE(s2 > s1);
+    ASSERT_GE(s2, s1);
+  }
+
+  {
+    int arr[] = { 1, 2, 3 };
+
+    AssertSpanOfThreeInts(arr);
+
+    Span<int> s1 = { &arr[0], 2 }; // shorter
+    Span<int> s2 = arr;            // longer
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+
+  {
+    int arr1[] = { 1, 2 }; // smaller
+    int arr2[] = { 2, 1 }; // bigger
+
+    Span<int> s1 = arr1;
+    Span<int> s2 = arr2;
+
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_NE(s1, s2);
+    ASSERT_NE(s2, s1);
+    ASSERT_LT(s1, s2);
+    ASSERT_FALSE(s2 < s1);
+    ASSERT_LE(s1, s2);
+    ASSERT_FALSE(s2 <= s1);
+    ASSERT_GT(s2, s1);
+    ASSERT_FALSE(s1 > s2);
+    ASSERT_GE(s2, s1);
+    ASSERT_FALSE(s1 >= s2);
+  }
+}
+
+SPAN_TEST(as_bytes)
+{
+  int a[] = { 1, 2, 3, 4 };
+
+  {
+    Span<const int> s = a;
+    ASSERT_EQ(s.Length(), 4U);
+    Span<const uint8_t> bs = AsBytes(s);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+
+  {
+    Span<int> s;
+    auto bs = AsBytes(s);
+    ASSERT_EQ(bs.Length(), s.Length());
+    ASSERT_EQ(bs.Length(), 0U);
+    ASSERT_EQ(bs.size_bytes(), 0U);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.data(), nullptr);
+  }
+
+  {
+    Span<int> s = a;
+    auto bs = AsBytes(s);
+    ASSERT_EQ(static_cast<const void*>(bs.data()),
+              static_cast<const void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+}
+
+SPAN_TEST(as_writable_bytes)
+{
+  int a[] = { 1, 2, 3, 4 };
+
+  {
+#ifdef CONFIRM_COMPILATION_ERRORS
+    // you should not be able to get writeable bytes for const objects
+    Span<const int> s = a;
+    ASSERT_EQ(s.Length(), 4U);
+    Span<const byte> bs = AsWritableBytes(s);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+#endif
+  }
+
+  {
+    Span<int> s;
+    auto bs = AsWritableBytes(s);
+    ASSERT_EQ(bs.Length(), s.Length());
+    ASSERT_EQ(bs.Length(), 0U);
+    ASSERT_EQ(bs.size_bytes(), 0U);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.data(), nullptr);
+  }
+
+  {
+    Span<int> s = a;
+    auto bs = AsWritableBytes(s);
+    ASSERT_EQ(static_cast<void*>(bs.data()), static_cast<void*>(s.data()));
+    ASSERT_EQ(bs.Length(), s.LengthBytes());
+  }
+}
+
+SPAN_TEST(fixed_size_conversions)
+{
+  int arr[] = { 1, 2, 3, 4 };
+
+  // converting to an Span from an equal size array is ok
+  Span<int, 4> s4 = arr;
+  ASSERT_EQ(s4.Length(), 4U);
+
+  // converting to dynamic_range is always ok
+  {
+    Span<int> s = s4;
+    ASSERT_EQ(s.Length(), s4.Length());
+    static_cast<void>(s);
+  }
+
+// initialization or assignment to static Span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 2> s = arr;
+  }
+  {
+    Span<int, 2> s2 = s4;
+    static_cast<void>(s2);
+  }
+#endif
+
+#if 0
+        // even when done dynamically
+        {
+            Span<int> s = arr;
+            auto f = [&]() {
+                Span<int, 2> s2 = s;
+                static_cast<void>(s2);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+#endif
+
+  // but doing so explicitly is ok
+
+  // you can convert statically
+  {
+    Span<int, 2> s2 = { arr, 2 };
+    static_cast<void>(s2);
+  }
+  {
+    Span<int, 1> s1 = s4.First<1>();
+    static_cast<void>(s1);
+  }
+
+  // ...or dynamically
+  {
+    // NB: implicit conversion to Span<int,1> from Span<int>
+    Span<int, 1> s1 = s4.First(1);
+    static_cast<void>(s1);
+  }
+
+#if 0
+        // initialization or assignment to static Span that requires size INCREASE is not ok.
+        int arr2[2] = {1, 2};
+#endif
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+  {
+    Span<int, 4> s3 = arr2;
+  }
+  {
+    Span<int, 2> s2 = arr2;
+    Span<int, 4> s4a = s2;
+  }
+#endif
+
+#if 0
+        {
+            auto f = [&]() {
+                Span<int, 4> _s4 = {arr2, 2};
+                static_cast<void>(_s4);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // this should fail - we are trying to assign a small dynamic Span to a fixed_size larger one
+        Span<int> av = arr2;
+        auto f = [&]() {
+            Span<int, 4> _s4 = av;
+            static_cast<void>(_s4);
+        };
+        CHECK_THROW(f(), fail_fast);
+#endif
+}
+
+#if 0
+    SPAN_TEST(interop_with_std_regex)
+    {
+        char lat[] = { '1', '2', '3', '4', '5', '6', 'E', 'F', 'G' };
+        Span<char> s = lat;
+        auto f_it = s.begin() + 7;
+
+        std::match_results<Span<char>::iterator> match;
+
+        std::regex_match(s.begin(), s.end(), match, std::regex(".*"));
+        ASSERT_EQ(match.ready());
+        ASSERT_TRUE(!match.empty());
+        ASSERT_TRUE(match[0].matched);
+        ASSERT_TRUE(match[0].first , s.begin());
+        ASSERT_EQ(match[0].second , s.end());
+
+        std::regex_search(s.begin(), s.end(), match, std::regex("F"));
+        ASSERT_TRUE(match.ready());
+        ASSERT_TRUE(!match.empty());
+        ASSERT_TRUE(match[0].matched);
+        ASSERT_EQ(match[0].first , f_it);
+        ASSERT_EQ(match[0].second , (f_it + 1));
+    }
+
+SPAN_TEST(interop_with_gsl_at)
+{
+  int arr[5] = { 1, 2, 3, 4, 5 };
+  Span<int> s{ arr };
+  ASSERT_EQ(at(s, 0) , 1 );
+ASSERT_EQ(at(s, 1) , 2U);
+}
+#endif
+
+SPAN_TEST(default_constructible)
+{
+  ASSERT_TRUE((std::is_default_constructible<Span<int>>::value));
+  ASSERT_TRUE((std::is_default_constructible<Span<int, 0>>::value));
+  ASSERT_TRUE((!std::is_default_constructible<Span<int, 42>>::value));
+}
diff --git a/mfbt/tests/gtest/moz.build b/mfbt/tests/gtest/moz.build
new file mode 100644
index 000000000..bd559d60b
--- /dev/null
+++ b/mfbt/tests/gtest/moz.build
@@ -0,0 +1,15 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+UNIFIED_SOURCES += [
+    'TestSpan.cpp',
+]
+
+#LOCAL_INCLUDES += [
+#    '../../base',
+#]
+
+FINAL_LIBRARY = 'xul-gtest'
diff --git a/mfbt/tests/moz.build b/mfbt/tests/moz.build
index bd25ab1d0..e69de5d75 100644
--- a/mfbt/tests/moz.build
+++ b/mfbt/tests/moz.build
@@ -4,6 +4,11 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+if not CONFIG['JS_STANDALONE']:
+    TEST_DIRS += [
+        'gtest',
+    ]
+
 CppUnitTests([
     'TestArray',
     'TestArrayUtils',
diff --git a/toolkit/content/license.html b/toolkit/content/license.html
index a348fdfa6..7221a8ae2 100644
--- a/toolkit/content/license.html
+++ b/toolkit/content/license.html
@@ -97,6 +97,7 @@
       <li><a href="about:license#gears">Google Gears License</a></li>
       <li><a href="about:license#gears-istumbler">Google Gears/iStumbler License</a></li>
       <li><a href="about:license#vp8">Google VP8 License</a></li>
+      <li><a href="about:license#gsl">GSL License</a></li>
       <li><a href="about:license#gyp">gyp License</a></li>
       <li><a href="about:license#halloc">halloc License</a></li>
       <li><a href="about:license#harfbuzz">HarfBuzz License</a></li>
@@ -3285,6 +3286,38 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
     <hr>
 
+    <h1><a id="gsl"></a>GSL License</h1>
+
+    <p>This license applies to <span class="path">mfbt/Span.h</span> and
+    <span class="path">mfbt/tests/gtest/TestSpan.cpp</span>.</p>
+    <!-- https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/LICENSE -->
+<pre>
+Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+
+This code is licensed under the MIT License (MIT).
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+</pre>
+
+
+    <hr>
+
     <h1><a id="gyp"></a>gyp License</h1>
 
     <p>This license applies to certain files in the directory
diff --git a/xpcom/glue/nsTArray.h b/xpcom/glue/nsTArray.h
index ca74a41f7..c86772a8e 100644
--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -19,6 +19,7 @@
 #include "mozilla/Move.h"
 #include "mozilla/ReverseIterator.h"
 #include "mozilla/TypeTraits.h"
+#include "mozilla/Span.h"
 
 #include <string.h>
 
@@ -1112,6 +1113,18 @@ public:
   const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
   const_reverse_iterator crend() const { return rend(); }
 
+  // Span integration
+
+  operator mozilla::Span<elem_type>()
+  {
+    return mozilla::Span<elem_type>(Elements(), Length());
+  }
+
+  operator mozilla::Span<const elem_type>() const
+  {
+    return mozilla::Span<const elem_type>(Elements(), Length());
+ }
+
   //
   // Search methods
   //
@@ -1336,6 +1349,16 @@ protected:
     return ReplaceElementsAt<Item, ActualAlloc>(
       aStart, aCount, aArray.Elements(), aArray.Length());
   }
+
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* ReplaceElementsAt(index_type aStart,
+                               size_type aCount,
+                               mozilla::Span<const Item> aSpan)
+  {
+    return ReplaceElementsAt<Item, ActualAlloc>(
+      aStart, aCount, aSpan.Elements(), aSpan.Length());
+  }
+
 public:
 
   template<class Item>
@@ -1347,6 +1370,15 @@ public:
     return ReplaceElementsAt<Item, FallibleAlloc>(aStart, aCount, aArray);
   }
 
+  template<class Item>
+  MOZ_MUST_USE elem_type* ReplaceElementsAt(index_type aStart,
+                                            size_type aCount,
+                                            mozilla::Span<const Item> aSpan,
+                                            const mozilla::fallible_t&)
+  {
+    return ReplaceElementsAt<Item, FallibleAlloc>(aStart, aCount, aSpan);
+  }
+
   // A variation on the ReplaceElementsAt method defined above.
 protected:
   template<class Item, typename ActualAlloc = Alloc>
@@ -1399,6 +1431,15 @@ protected:
     return ReplaceElementsAt<Item, ActualAlloc>(
       aIndex, 0, aArray.Elements(), aArray.Length());
   }
+
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* InsertElementsAt(index_type aIndex,
+                              mozilla::Span<const Item> aSpan)
+  {
+    return ReplaceElementsAt<Item, ActualAlloc>(
+      aIndex, 0, aSpan.Elements(), aSpan.Length());
+  }
+
 public:
 
   template<class Item, class Allocator>
@@ -1425,6 +1466,14 @@ public:
     return InsertElementAt<FallibleAlloc>(aIndex);
   }
 
+  template<class Item>
+  MOZ_MUST_USE elem_type* InsertElementsAt(index_type aIndex,
+                                           mozilla::Span<const Item> aSpan,
+                                           const mozilla::fallible_t&)
+  {
+    return InsertElementsAt<Item, FallibleAlloc>(aIndex, aSpan);
+  }
+
   // Insert a new element, move constructing if possible.
 protected:
   template<class Item, typename ActualAlloc = Alloc>
@@ -1526,6 +1575,13 @@ protected:
   template<class Item, typename ActualAlloc = Alloc>
   elem_type* AppendElements(const Item* aArray, size_type aArrayLen);
 
+  template<class Item, typename ActualAlloc = Alloc>
+  elem_type* AppendElements(mozilla::Span<const Item> aSpan)
+  {
+    return AppendElements<Item, FallibleAlloc>(aSpan.Elements(),
+                                               aSpan.Length());
+  }
+
 public:
 
   template<class Item>
@@ -1536,6 +1592,15 @@ public:
     return AppendElements<Item, FallibleAlloc>(aArray, aArrayLen);
   }
 
+  template<class Item>
+  /* MOZ_MUST_USE */
+  elem_type* AppendElements(mozilla::Span<const Item> aSpan,
+                            const mozilla::fallible_t&)
+  {
+    return AppendElements<Item, FallibleAlloc>(aSpan.Elements(),
+                                               aSpan.Length());
+  }
+
   // A variation on the AppendElements method defined above.
 protected:
   template<class Item, class Allocator, typename ActualAlloc = Alloc>
@@ -2347,6 +2412,25 @@ struct nsTArray_CopyChooser<AutoTArray<E, N>>
   typedef nsTArray_CopyWithConstructors<AutoTArray<E, N>> Type;
 };
 
+// Span integration
+namespace mozilla {
+
+template<class ElementType, class TArrayAlloc>
+Span<ElementType>
+MakeSpan(nsTArray_Impl<ElementType, TArrayAlloc>& aTArray)
+{
+  return aTArray;
+}
+
+template<class ElementType, class TArrayAlloc>
+Span<const ElementType>
+MakeSpan(const nsTArray_Impl<ElementType, TArrayAlloc>& aTArray)
+{
+  return aTArray;
+}
+
+} // namespace mozilla
+
 // Assert that AutoTArray doesn't have any extra padding inside.
 //
 // It's important that the data stored in this auto array takes up a multiple of
diff --git a/xpcom/string/nsTSubstring.h b/xpcom/string/nsTSubstring.h
index a08036b1f..53b4fb9a8 100644
--- a/xpcom/string/nsTSubstring.h
+++ b/xpcom/string/nsTSubstring.h
@@ -7,6 +7,8 @@
 
 #include "mozilla/Casting.h"
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/IntegerTypeTraits.h"
+#include "mozilla/Span.h"
 
 #ifndef MOZILLA_INTERNAL_API
 #error Cannot use internal string classes without MOZILLA_INTERNAL_API defined. Use the frozen header nsStringAPI.h instead.
@@ -798,6 +800,68 @@ public:
   }
 #endif
 
+  /**
+   * Span integration
+   */
+
+  operator mozilla::Span<char_type>()
+  {
+    return mozilla::MakeSpan(BeginWriting(), Length());
+  }
+
+  operator mozilla::Span<const char_type>() const
+  {
+    return mozilla::MakeSpan(BeginReading(), Length());
+  }
+
+  void Append(mozilla::Span<const char_type> aSpan)
+  {
+    auto len = aSpan.Length();
+    MOZ_RELEASE_ASSERT(len <= mozilla::MaxValue<size_type>::value);
+    Append(aSpan.Elements(), len);
+  }
+
+  MOZ_MUST_USE bool Append(mozilla::Span<const char_type> aSpan,
+                           const fallible_t& aFallible)
+  {
+    auto len = aSpan.Length();
+    if (len > mozilla::MaxValue<size_type>::value) {
+      return false;
+    }
+    return Append(aSpan.Elements(), len, aFallible);
+  }
+
+#if !defined(CharT_is_PRUnichar)
+  operator mozilla::Span<uint8_t>()
+  {
+    return mozilla::MakeSpan(reinterpret_cast<uint8_t*>(BeginWriting()),
+                             Length());
+  }
+
+  operator mozilla::Span<const uint8_t>() const
+  {
+    return mozilla::MakeSpan(reinterpret_cast<const uint8_t*>(BeginReading()),
+                             Length());
+  }
+
+  void Append(mozilla::Span<const uint8_t> aSpan)
+  {
+    auto len = aSpan.Length();
+    MOZ_RELEASE_ASSERT(len <= mozilla::MaxValue<size_type>::value);
+    Append(reinterpret_cast<const char*>(aSpan.Elements()), len);
+  }
+
+  MOZ_MUST_USE bool Append(mozilla::Span<const uint8_t> aSpan,
+                           const fallible_t& aFallible)
+  {
+    auto len = aSpan.Length();
+    if (len > mozilla::MaxValue<size_type>::value) {
+      return false;
+    }
+    return Append(
+      reinterpret_cast<const char*>(aSpan.Elements()), len, aFallible);
+  }
+#endif
 
   /**
    * string data is never null, but can be marked void.  if true, the
@@ -1184,3 +1248,22 @@ operator>(const nsTSubstring_CharT::base_string_type& aLhs,
 {
   return Compare(aLhs, aRhs) > 0;
 }
+
+/**
+ * Span integration
+ */
+namespace mozilla {
+
+inline Span<CharT>
+MakeSpan(nsTSubstring_CharT& aString)
+{
+  return aString;
+}
+
+inline Span<const CharT>
+MakeSpan(const nsTSubstring_CharT& aString)
+{
+  return aString;
+}
+
+} // namespace mozilla