--- a/widget/PuppetWidget.cpp
+++ b/widget/PuppetWidget.cpp
@@ -1145,17 +1145,18 @@ PuppetWidget::MemoryPressureObserver::Ob
                                               const char* aTopic,
                                               const char16_t* aData)
 {
   if (!mWidget) {
     return NS_OK;
   }
 
   if (strcmp("memory-pressure", aTopic) == 0 &&
-      !NS_LITERAL_STRING("lowering-priority").Equals(aData)) {
+      !StringBeginsWith(nsDependentString(aData),
+                        NS_LITERAL_STRING("low-memory-ongoing"))) {
     if (!mWidget->mVisible && mWidget->mLayerManager &&
         XRE_IsContentProcess()) {
       mWidget->mLayerManager->ClearCachedResources();
     }
   }
   return NS_OK;
 }
 

--- a/xpcom/base/nsIMemory.idl
+++ b/xpcom/base/nsIMemory.idl
@@ -35,27 +35,16 @@
  * "-no-forward"
  * This is appended to the above two parameters when the resulting
  * notification should not be forwarded to the child processes.
  *
  * "heap-minimize"
  * This will be passed as the extra data when the pressure 
  * observer is being asked to flush because of a heap minimize 
  * call.
- *
- * "alloc-failure"
- * This will be passed as the extra data when the pressure 
- * observer has been asked to flush because a malloc() or 
- * realloc() has failed.
- *
- * "lowering-priority"
- * This will be passed as the extra data when the priority of a child
- * process is lowered. The pressure observers could take the chance to
- * clear caches that could be easily regenerated. This type of
- * notification only appears in child processes.
  */
 
 [scriptable, uuid(1e004834-6d8f-425a-bc9c-a2812ed43bb7)]
 interface nsIMemory : nsISupports
 {
     /**
      * Attempts to shrink the heap.
      * @param immediate - if true, heap minimization will occur