--- a/image/src/DiscardTracker.cpp
+++ b/image/src/DiscardTracker.cpp
@@ -40,18 +40,16 @@ DiscardTimeoutChangedCallback(const char
 {
   DiscardTracker::ReloadTimeout();
   return 0;
 }
 
 nsresult
 DiscardTracker::Reset(Node *node)
 {
-  EnsureMainThread();
-
   // We shouldn't call Reset() with a null |img| pointer, on images which can't
   // be discarded, or on animated images (which should be marked as
   // non-discardable, anyway).
   MOZ_ASSERT(node->img);
   MOZ_ASSERT(node->img->CanDiscard());
   MOZ_ASSERT(!node->img->mAnim);
 
   // Initialize the first time through.
@@ -81,47 +79,41 @@ DiscardTracker::Reset(Node *node)
   NS_ENSURE_SUCCESS(rv,rv);
 
   return NS_OK;
 }
 
 void
 DiscardTracker::Remove(Node *node)
 {
-  EnsureMainThread();
-
   if (node->isInList())
     node->remove();
 
   if (sDiscardableImages.isEmpty())
     DisableTimer();
 }
 
 /**
  * Shut down the tracker, deallocating the timer.
  */
 void
 DiscardTracker::Shutdown()
 {
-  EnsureMainThread();
-
   if (sTimer) {
     sTimer->Cancel();
     sTimer = NULL;
   }
 }
 
 /*
  * Discard all the images we're tracking.
  */
 void
 DiscardTracker::DiscardAll()
 {
-  EnsureMainThread();
-
   if (!sInitialized)
     return;
 
   // Be careful: Calling Discard() on an image might cause it to be removed
   // from the list!
   Node *n;
   while ((n = sDiscardableImages.popFirst())) {
     n->img->Discard();
@@ -129,39 +121,26 @@ DiscardTracker::DiscardAll()
 
   // The list is empty, so there's no need to leave the timer on.
   DisableTimer();
 }
 
 void
 DiscardTracker::InformAllocation(PRInt64 bytes)
 {
-  EnsureMainThread();
-
   // This function is called back e.g. from RasterImage::Discard(); be careful!
 
   sCurrentDecodedImageBytes += bytes;
   MOZ_ASSERT(sCurrentDecodedImageBytes >= 0);
 
   // If we're using too much memory for decoded images, MaybeDiscardSoon will
   // enqueue a callback to discard some images.
   MaybeDiscardSoon();
 }
 
-void
-DiscardTracker::EnsureMainThread()
-{
-  // NS_RUNTIMEABORT is a fatal crash even in release builds.  We need to crash
-  // release builds here in order to investigate bug 745141 -- we're being
-  // called from off main thread, but we don't know how!
-  if (!NS_IsMainThread()) {
-    NS_RUNTIMEABORT("Must be on main thread!");
-  }
-}
-
 /**
  * Initialize the tracker.
  */
 nsresult
 DiscardTracker::Initialize()
 {
   // Watch the timeout pref for changes.
   Preferences::RegisterCallback(DiscardTimeoutChangedCallback,

--- a/image/src/DiscardTracker.h
+++ b/image/src/DiscardTracker.h
@@ -95,18 +95,16 @@ class DiscardTracker
     static nsresult Initialize();
     static void ReloadTimeout();
     static nsresult EnableTimer();
     static void DisableTimer();
     static void MaybeDiscardSoon();
     static void TimerCallback(nsITimer *aTimer, void *aClosure);
     static void DiscardNow();
 
-    static void EnsureMainThread();
-
     static LinkedList<Node> sDiscardableImages;
     static nsCOMPtr<nsITimer> sTimer;
     static bool sInitialized;
     static bool sTimerOn;
     static bool sDiscardRunnablePending;
     static PRInt64 sCurrentDecodedImageBytes;
     static PRUint32 sMinDiscardTimeoutMs;
     static PRUint32 sMaxDecodedImageKB;