--- a/gfx/thebes/gfxMacPlatformFontList.mm
+++ b/gfx/thebes/gfxMacPlatformFontList.mm
@@ -59,16 +59,17 @@
 #include "nsAppDirectoryServiceDefs.h"
 #include "nsISimpleEnumerator.h"
 #include "nsCharTraits.h"
 #include "nsCocoaFeatures.h"
 #include "nsCocoaUtils.h"
 #include "gfxFontConstants.h"
 
 #include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/ContentParent.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/gfx/2D.h"
 
 #include <unistd.h>
 #include <time.h>
@@ -983,34 +984,42 @@ gfxMacPlatformFontList::gfxMacPlatformFo
     nsCOMPtr<nsIFile> langFonts(do_CreateInstance(NS_LOCAL_FILE_CONTRACTID, &rv));
     if (NS_SUCCEEDED(rv)) {
         rv = langFonts->InitWithNativePath(NS_LITERAL_CSTRING(LANG_FONTS_DIR));
         if (NS_SUCCEEDED(rv)) {
             ActivateFontsFromDir(langFonts);
         }
     }
 
-    ::CFNotificationCenterAddObserver(::CFNotificationCenterGetLocalCenter(),
-                                      this,
-                                      RegisteredFontsChangedNotificationCallback,
-                                      kCTFontManagerRegisteredFontsChangedNotification,
-                                      0,
-                                      CFNotificationSuspensionBehaviorDeliverImmediately);
+    // Only the parent process listens for OS font-changed notifications;
+    // after rebuilding its list, it will update the content processes.
+    if (XRE_IsParentProcess()) {
+        ::CFNotificationCenterAddObserver(
+            ::CFNotificationCenterGetLocalCenter(),
+            this,
+            RegisteredFontsChangedNotificationCallback,
+            kCTFontManagerRegisteredFontsChangedNotification,
+            0,
+            CFNotificationSuspensionBehaviorDeliverImmediately);
+    }
 
     // cache this in a static variable so that MacOSFontFamily objects
     // don't have to repeatedly look it up
     sFontManager = [NSFontManager sharedFontManager];
 }
 
 gfxMacPlatformFontList::~gfxMacPlatformFontList()
 {
-    ::CFNotificationCenterRemoveObserver(::CFNotificationCenterGetLocalCenter(),
-                                         this,
-                                         kCTFontManagerRegisteredFontsChangedNotification,
-                                         0);
+    if (XRE_IsParentProcess()) {
+        ::CFNotificationCenterRemoveObserver(
+            ::CFNotificationCenterGetLocalCenter(),
+            this,
+            kCTFontManagerRegisteredFontsChangedNotification,
+            0);
+    }
 
     if (mDefaultFont) {
         ::CFRelease(mDefaultFont);
     }
 }
 
 void
 gfxMacPlatformFontList::AddFamily(const nsAString& aFamilyName,
@@ -1095,19 +1104,18 @@ gfxMacPlatformFontList::InitFontListForP
 
     // reset system font list
     mSystemFontFamilies.Clear();
 
     if (XRE_IsContentProcess()) {
         // Content process: use font list passed from the chrome process via
         // the GetXPCOMProcessAttributes message, because it's much faster than
         // querying Core Text again in the child.
-        mozilla::dom::ContentChild* cc =
-            mozilla::dom::ContentChild::GetSingleton();
-        for (SystemFontListEntry& fle : cc->SystemFontList()) {
+        auto& fontList = dom::ContentChild::GetSingleton()->SystemFontList();
+        for (SystemFontListEntry& fle : fontList) {
             MOZ_ASSERT(fle.type() ==
                        SystemFontListEntry::Type::TFontFamilyListEntry);
             FontFamilyListEntry& ffe(fle);
             switch (ffe.entryType()) {
             case kStandardFontFamily:
                 AddFamily(ffe.familyName(), false);
                 break;
             case kHiddenSystemFontFamily:
@@ -1117,23 +1125,20 @@ gfxMacPlatformFontList::InitFontListForP
                 mSystemTextFontFamilyName = ffe.familyName();
                 break;
             case kDisplaySizeSystemFontFamily:
                 mSystemDisplayFontFamilyName = ffe.familyName();
                 mUseSizeSensitiveSystemFont = true;
                 break;
             }
         }
-        // The ContentChild doesn't need the font list any longer.
-        cc->SystemFontList().Clear();
-    }
-
-    // If this is the chrome process, or if for some reason we failed to get
-    // a usable list above, get the available fonts from Core Text.
-    if (!mFontFamilies.Count()) {
+        fontList.Clear();
+    } else {
+        // We're not a content process, so get the available fonts directly
+        // from Core Text.
         InitSystemFontNames();
         CFArrayRef familyNames = CTFontManagerCopyAvailableFontFamilyNames();
         for (NSString* familyName in (NSArray*)familyNames) {
             AddFamily((CFStringRef)familyName);
         }
         CFRelease(familyNames);
     }
 
@@ -1342,16 +1347,18 @@ gfxMacPlatformFontList::RegisteredFontsC
 
     gfxMacPlatformFontList* fl = static_cast<gfxMacPlatformFontList*>(observer);
 
     // xxx - should be carefully pruning the list of fonts, not rebuilding it from scratch
     fl->UpdateFontList();
 
     // modify a preference that will trigger reflow everywhere
     fl->ForceGlobalReflow();
+
+    mozilla::dom::ContentParent::NotifyUpdatedFonts();
 }
 
 gfxFontEntry*
 gfxMacPlatformFontList::PlatformGlobalFontFallback(const uint32_t aCh,
                                                    Script aRunScript,
                                                    const gfxFontStyle* aMatchStyle,
                                                    gfxFontFamily** aMatchedFamily)
 {