diff --git a/gfx/thebes/gfxFontInfoLoader.cpp b/gfx/thebes/gfxFontInfoLoader.cpp
index ee32a961e45..3b33725495c 100644
--- a/gfx/thebes/gfxFontInfoLoader.cpp
+++ b/gfx/thebes/gfxFontInfoLoader.cpp
@@ -12,6 +12,12 @@
 using namespace mozilla;
 using services::GetObserverService;
 
+#define LOG_FONTINIT(args) MOZ_LOG(gfxPlatform::GetLog(eGfxLog_fontinit), \
+                               LogLevel::Debug, args)
+#define LOG_FONTINIT_ENABLED() MOZ_LOG_TEST( \
+                                   gfxPlatform::GetLog(eGfxLog_fontinit), \
+                                   LogLevel::Debug)
+
 void
 FontInfoData::Load()
 {
@@ -57,6 +63,21 @@ class AsyncFontInfoLoader : public nsRunnable {
     nsRefPtr<FontInfoLoadCompleteEvent> mCompleteEvent;
 };
 
+class ShutdownThreadEvent : public nsRunnable {
+    virtual ~ShutdownThreadEvent() {}
+
+    NS_DECL_ISUPPORTS_INHERITED
+
+    explicit ShutdownThreadEvent(nsIThread* aThread) : mThread(aThread) {}
+    NS_IMETHOD Run() override {
+        mThread->Shutdown();
+        return NS_OK;
+    }
+    nsCOMPtr<nsIThread> mThread;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED0(ShutdownThreadEvent, nsRunnable);
+
 // runs on main thread after async font info loading is done
 nsresult
 FontInfoLoadCompleteEvent::Run()
@@ -106,6 +127,9 @@ gfxFontInfoLoader::StartLoader(uint32_t aDelay, uint32_t aInterval)
 {
     mInterval = aInterval;
 
+    NS_ASSERTION(!mFontInfo,
+                 "fontinfo should be null when starting font loader");
+
     // sanity check
     if (mState != stateInitial &&
         mState != stateTimerOff &&
@@ -149,6 +173,11 @@ gfxFontInfoLoader::StartLoader(uint32_t aDelay, uint32_t aInterval)
     nsCOMPtr<nsIRunnable> loadEvent = new AsyncFontInfoLoader(mFontInfo);
 
     mFontLoaderThread->Dispatch(loadEvent.forget(), NS_DISPATCH_NORMAL);
+
+    if (LOG_FONTINIT_ENABLED()) {
+        LOG_FONTINIT(("(fontinit) fontloader started (fontinfo: %p)\n",
+                      mFontInfo.get()));
+    }
 }
 
 void
@@ -159,7 +188,7 @@ gfxFontInfoLoader::FinalizeLoader(FontInfoData *aFontInfo)
     // thread has already Shutdown(), and likely before processing
     // the Shutdown event it handled the load event and sent back
     // our Completion event, thus we end up here.
-    if (mState != stateAsyncLoad) {
+    if (mState != stateAsyncLoad || mFontInfo != aFontInfo) {
         return;
     }
 
@@ -189,11 +218,8 @@ gfxFontInfoLoader::CancelLoader()
         mTimer = nullptr;
     }
     if (mFontLoaderThread) {
-        // NOTE: Shutdown() runs the event loop, and we can get timer events
-        // ensure that we can't try to do this twice!
-        nsCOMPtr<nsIThread> temp;
-        temp.swap(mFontLoaderThread);
-        temp->Shutdown();
+        NS_DispatchToMainThread(new ShutdownThreadEvent(mFontLoaderThread));
+        mFontLoaderThread = nullptr;
     }
     RemoveShutdownObserver();
     CleanupLoader();
diff --git a/gfx/thebes/gfxPlatformFontList.cpp b/gfx/thebes/gfxPlatformFontList.cpp
index 2f4890c0b2f..371f60fb0cb 100644
--- a/gfx/thebes/gfxPlatformFontList.cpp
+++ b/gfx/thebes/gfxPlatformFontList.cpp
@@ -195,6 +195,10 @@ gfxPlatformFontList::~gfxPlatformFontList()
 nsresult
 gfxPlatformFontList::InitFontList()
 {
+    if (LOG_FONTINIT_ENABLED()) {
+        LOG_FONTINIT(("(fontinit) system fontlist initialization\n"));
+    }
+
     // rebuilding fontlist so clear out font/word caches
     gfxFontCache *fontCache = gfxFontCache::GetCache();
     if (fontCache) {