2 files changed, 25 insertions, 15 deletions

diff --git a/netwerk/protocol/http/nsHttpHandler.cpp b/netwerk/protocol/http/nsHttpHandler.cpp
index f9bcc391d..89f09190d 100644
--- a/netwerk/protocol/http/nsHttpHandler.cpp
+++ b/netwerk/protocol/http/nsHttpHandler.cpp
@@ -203,6 +203,7 @@ nsHttpHandler::nsHttpHandler()
     , mCompatFirefoxEnabled(false)
     , mCompatFirefoxVersion("52.9")
     , mUserAgentIsDirty(true)
+    , mAcceptLanguagesIsDirty(true)
     , mPromptTempRedirect(true)
     , mEnablePersistentHttpsCaching(false)
     , mDoNotTrackEnabled(false)
@@ -419,6 +420,7 @@ nsHttpHandler::Init()
         obsService->AddObserver(this, "browser:purge-session-history", true);
         obsService->AddObserver(this, NS_NETWORK_LINK_TOPIC, true);
         obsService->AddObserver(this, "application-background", true);
+        obsService->AddObserver(this, "string-bundles-have-flushed", true);
     }
 
     MakeNewRequestTokenBucket();
@@ -489,8 +491,13 @@ nsHttpHandler::AddStandardRequestHeaders(nsHttpRequestHead *request, bool isSecu
 
     // Add the "Accept-Language" header.  This header is also exposed to the
     // service worker.
+    if (mAcceptLanguagesIsDirty) {
+        rv = SetAcceptLanguages();
+        MOZ_ASSERT(NS_SUCCEEDED(rv));
+    }
+
+    // Add the "Accept-Language" header
     if (!mAcceptLanguages.IsEmpty()) {
-        // Add the "Accept-Language" header
         rv = request->SetHeader(nsHttp::Accept_Language, mAcceptLanguages,
                                 false,
                                 nsHttpHeaderArray::eVarietyRequestOverride);
@@ -1511,16 +1518,10 @@ nsHttpHandler::PrefsChanged(nsIPrefBranch *prefs, const char *pref)
     //
 
     if (PREF_CHANGED(INTL_ACCEPT_LANGUAGES)) {
-        nsCOMPtr<nsIPrefLocalizedString> pls;
-        prefs->GetComplexValue(INTL_ACCEPT_LANGUAGES,
-                                NS_GET_IID(nsIPrefLocalizedString),
-                                getter_AddRefs(pls));
-        if (pls) {
-            nsXPIDLString uval;
-            pls->ToString(getter_Copies(uval));
-            if (uval)
-                SetAcceptLanguages(NS_ConvertUTF16toUTF8(uval).get());
-        }
+        // We don't want to set the new accept languages here since
+        // this pref is a complex type and it may be racy with flushing
+        // string resources.
+        mAcceptLanguagesIsDirty = true;
     }
 
     //
@@ -1897,12 +1898,18 @@ PrepareAcceptLanguages(const char *i_AcceptLanguages, nsACString &o_AcceptLangua
 }
 
 nsresult
-nsHttpHandler::SetAcceptLanguages(const char *aAcceptLanguages)
+nsHttpHandler::SetAcceptLanguages()
 {
+    mAcceptLanguagesIsDirty = false;
+
+    const nsAdoptingCString& acceptLanguages =
+        Preferences::GetLocalizedCString(INTL_ACCEPT_LANGUAGES);
+
     nsAutoCString buf;
-    nsresult rv = PrepareAcceptLanguages(aAcceptLanguages, buf);
-    if (NS_SUCCEEDED(rv))
+    nsresult rv = PrepareAcceptLanguages(acceptLanguages.get(), buf);
+    if (NS_SUCCEEDED(rv)) {
         mAcceptLanguages.Assign(buf);
+    }
     return rv;
 }
 
@@ -2233,6 +2240,8 @@ nsHttpHandler::Observe(nsISupports *subject,
         if (mConnMgr) {
             mConnMgr->DoShiftReloadConnectionCleanup(nullptr);
         }
+    } else if (!strcmp(topic, "string-bundles-have-flushed")) {
+        mAcceptLanguagesIsDirty = true;
     }
 
     return NS_OK;
diff --git a/netwerk/protocol/http/nsHttpHandler.h b/netwerk/protocol/http/nsHttpHandler.h
index 0904af893..848dd25b1 100644
--- a/netwerk/protocol/http/nsHttpHandler.h
+++ b/netwerk/protocol/http/nsHttpHandler.h
@@ -384,7 +384,7 @@ private:
     void     PrefsChanged(nsIPrefBranch *prefs, const char *pref);
 
     nsresult SetAccept(const char *);
-    nsresult SetAcceptLanguages(const char *);
+    nsresult SetAcceptLanguages();
     nsresult SetAcceptEncodings(const char *, bool mIsSecure);
 
     nsresult InitConnectionMgr();
@@ -491,6 +491,7 @@ private:
     nsCString      mUserAgent;
     nsXPIDLCString mUserAgentOverride;
     bool           mUserAgentIsDirty; // true if mUserAgent should be rebuilt
+    bool           mAcceptLanguagesIsDirty;
 
 
     bool           mPromptTempRedirect;