To upgrade to a new revision of libjpeg-turbo, do the following:

* Check out libjpeg-turbo from git:

    $ git clone https://github.com/libjpeg-turbo/libjpeg-turbo.git

* In a clean clone of mozilla-central, run the update script (tag defaults to HEAD):

    $ ./media/update-libjpeg.sh /path/to/libjpeg-turbo [tag]

  and fix up any rejects from applying the Mozilla specific patches at the end
  of that script.

* Since libjpeg-turbo normally creates jconfig.h and jconfigint.h at build time
  and we use pre-generated versions, changes to jconfig.h.in and jconfigint.h.in
  should be looked for and noted for later inclusion.

* Now look through the new files and rm any which are npotb.  When I upgraded
  to libjpeg-turbo 1.1.0, the only files I kept which didn't match

    *.c  *.h *.asm *.inc

  were README and README-turbo.

  You can easily look for all non *.c, *.h, *.asm, and *.inc files by running

    $ hg status -nu | grep -v '\(c\|h\|asm\|inc\|md\|ijg\)$'

  Once you're comfortable that you're only deleting files you want to delete
  (and you've hg add'ed the files you want to keep), you can nuke the remaining
  files with

    $ hg status -nu | grep -v '\(c\|h\|asm\|inc\|md\|ijg\)$' | xargs rm

  A helpful command for finding the *.c files which aren't *currently* part of
  the build is

    diff <(ls *.c | sort) <(grep -o '\w*\.c' Makefile.in | sort)

  Of course, libjpeg-turbo might have added some new source files, so you'll
  have to look though and figure out which of these files to keep.

* Update jconfig.h and jconfigint.h as noted previously.

* Update moz.build to build any new files.

* Finally, tell hg that we've added or removed some files:

    $ hg addremove

== September 22, 2016 (libjpeg-turbo v1.5.1 cb88e5da8003afcdc443b787fdcb77285e5a8a02 2016-09-20) ==

* Updated to v1.5.1 release.

== June 23, 2016 (libjpeg-turbo v1.5.0 3ff13e651bbe6de9c6f15d05235d1d4f26f63ffc 2016-05-31) ==

* Updated to v1.5.0 release.

== October 5, 2015 (libjpeg-turbo v1.4.2 d8da49effe6460d55239c4c009c57f42d8e4a494 2015-09-21) ==

* Updated to v1.4.2 release.

== January 15, 2015 (libjpeg-turbo v1.4.0 r1481 2015-01-07) ==

* Updated to v1.4.0 release.

== March 24, 2014 (libjpeg-turbo v1.3.1 r1205 2014-03-22) ==

* Updated to v1.3.1 release.

== November 25, 2013 ==

* Fix bug 891693.

== June 4, 2013 (libjpeg-turbo v1.3.0 r988 2013-05-25) ==

* Updated to v1.3.0 release.

== December 12, 2012 ==

* Replace the runtime computed jpeg_nbits_table with constants in
  jpeg_nbits_table.h to make it shareable among processes. (bug 815473)

== October 13, 2012 ==

* Modified config.h to use MOZ_ALWAYS_INLINE (bug 800106).

== July 4, 2012 (libjpeg-turbo v1.2.1 r853 2012-06-30) ==

* Updated to v1.2.1 stable release.

== June 5, 2012 (libjpeg-turbo v1.2.x branch, r831 2012-05-30) ==

* Updated to latest version on v1.2.x branch (bug 759891).

== February 10, 2012 (libjpeg-turbo v1.2.0 r807 2012-02-10) ==

* Imported jchuff.c, jdhuff.c, jdhuff.h under new licensing.

* Created mozilla.diff for the required jmorecfg.h changes and to allow for any
  future changes made by Mozilla to upstream files.

* Removed the following files which are unused by the Mozilla build:

    cderror.h, cdjpeg.h, jconfig.h.in, transupp.h, simd/jsimdcfg.inc.h


== March 28, 2011 (initial commit, libjpeg-turbo v1.1.0 r469 2011-02-27) ==

* Modified jmorecfg.h to define UINT8, UINT16, INT16, and INT32 in terms of
  prtypes to fix a build error on Windows.

* Defined INLINE as NS_ALWAYS_INLINE in jconfig.h.

* Removed the following files which are licensed under the wxWindows license:

    bmp.c, bmp.h, jpegut.c, jpgtest.cxx, rrtimer.h, rrutil.h, turbojpeg.h,
    turbojpegl.c

* Reverted the following files to what was previously in Mozilla's tree
  (nominally libjpeg 6.2):

    jchuff.c, jdhuff.c, jdhuff.h

  since the versions of these files in libjpeg-turbo are also under the
  wxWindows license.  (It would have been nicer to revert them to the new
  libjpeg-8b code, but that doesn't easily integrate with libjpeg-turbo.)