diff --git a/widget/src/mac/nsAppShell.cpp b/widget/src/mac/nsAppShell.cpp
index 251e2d21eafc..7c2bfd726077 100644
--- a/widget/src/mac/nsAppShell.cpp
+++ b/widget/src/mac/nsAppShell.cpp
@@ -84,6 +84,15 @@ NS_IMETHODIMP nsAppShell::Create(int* argc, char ** argv)
 	mMacSink = auto_ptr<nsMacMessageSink>( new nsMacMessageSink() );
 	nsIToolkit* toolkit = mToolkit.get();
 	mMacPump = auto_ptr<nsMacMessagePump>( new nsMacMessagePump(static_cast<nsToolkit*>(toolkit), mMacSink.get()) );
+  mMacMemoryCushion = auto_ptr<nsMacMemoryCushion>( new nsMacMemoryCushion() );  
+
+  if (!mMacSink.get() || !mMacPump.get() || !mMacMemoryCushion.get())
+    return NS_ERROR_OUT_OF_MEMORY;
+  
+  OSErr err = mMacMemoryCushion->Init(nsMacMemoryCushion::kMemoryReserveSize);
+  if (err != noErr)
+    return NS_ERROR_FAILURE;
+  
 	return NS_OK;
 }
 
@@ -97,6 +106,7 @@ NS_IMETHODIMP nsAppShell::Run(void)
 	if (!mMacPump.get())
 		return NS_ERROR_NOT_INITIALIZED;
 
+  mMacMemoryCushion->StartRepeating();
 	mMacPump->StartRunning();
 	mMacPump->DoMessagePump();
 
diff --git a/widget/src/mac/nsAppShell.h b/widget/src/mac/nsAppShell.h
index 8b0140437eab..21918a8930fd 100644
--- a/widget/src/mac/nsAppShell.h
+++ b/widget/src/mac/nsAppShell.h
@@ -41,6 +41,7 @@ using std::auto_ptr;
 
 class nsMacMessagePump;
 class nsMacMessageSink;
+class nsMacMemoryCushion;
 class nsIToolkit;
 
 
@@ -57,7 +58,8 @@ class nsAppShell : public nsIAppShell
     nsDispatchListener             *mDispatchListener;    // note: we don't own this, but it can be NULL
     nsCOMPtr<nsIToolkit>           mToolkit;
     auto_ptr<nsMacMessagePump>     mMacPump;
-    auto_ptr<nsMacMessageSink>     mMacSink;             //€€€ this will be COM, so use scc's COM_auto_ptr
+    auto_ptr<nsMacMessageSink>     mMacSink;             // this will be COM, so use scc's COM_auto_ptr
+    auto_ptr<nsMacMemoryCushion>    mMacMemoryCushion;
     PRBool                         mExitCalled;
 	static PRBool                  mInitializedToolbox;
 };
diff --git a/widget/src/mac/nsToolkit.cpp b/widget/src/mac/nsToolkit.cpp
index e824e742c75e..78b0ce15863f 100644
--- a/widget/src/mac/nsToolkit.cpp
+++ b/widget/src/mac/nsToolkit.cpp
@@ -30,7 +30,8 @@
 #include "nsIEventQueue.h"
 #include "nsIEventQueueService.h"
 #include "nsIServiceManager.h"
-
+#include "nsIImageManager.h"
+#include "nsGfxCIID.h"
 
 //#define MAC_PL_EVENT_TWEAKING
 
@@ -38,6 +39,7 @@
 static NS_DEFINE_CID(kEventQueueCID,  NS_EVENTQUEUE_CID);
 static NS_DEFINE_CID(kEventQueueServiceCID,  NS_EVENTQUEUESERVICE_CID);
 
+static NS_DEFINE_IID(kImageManagerCID, NS_IMAGEMANAGER_CID);
 
 static nsMacNSPREventQueueHandler*	gEventQueueHandler = nsnull;
 
@@ -285,3 +287,70 @@ NS_METHOD NS_GetCurrentToolkit(nsIToolkit* *aResult)
   return rv;
 }
 
+#pragma mark -
+
+Handle nsMacMemoryCushion::sMemoryReserve;
+
+nsMacMemoryCushion::nsMacMemoryCushion()
+{
+}
+
+nsMacMemoryCushion::~nsMacMemoryCushion()
+{
+  ::SetGrowZone(nsnull);
+  if (sMemoryReserve)
+    ::DisposeHandle(sMemoryReserve);
+}
+
+
+OSErr nsMacMemoryCushion::Init(Size reserveSize)
+{
+  sMemoryReserve = ::NewHandle(reserveSize);
+  if (sMemoryReserve == nsnull)
+    return ::MemError();
+  
+	::SetGrowZone(NewGrowZoneProc(GrowZoneProc));
+	return noErr;
+}
+
+
+void nsMacMemoryCushion::RepeatAction(const EventRecord &aMacEvent)
+{
+  if (!RecoverMemoryReserve(kMemoryReserveSize))
+  {
+    nsMemory::HeapMinimize();
+    
+    // until imglib implements nsIMemoryPressureObserver (bug 46337)
+    // manually flush the imglib cache here
+    nsCOMPtr<nsIImageManager> imageManager = do_GetService(kImageManagerCID);
+    if (imageManager)
+    {
+      imageManager->FlushCache();
+    }    
+  }
+}
+
+
+Boolean nsMacMemoryCushion::RecoverMemoryReserve(Size reserveSize)
+{
+  if (!sMemoryReserve) return true;     // not initted yet
+  if (*sMemoryReserve != nsnull) return true;   // everything is OK
+  
+  ::ReallocateHandle(sMemoryReserve, reserveSize);
+  if (::MemError() != noErr) return false;
+  return true;
+}
+
+pascal long nsMacMemoryCushion::GrowZoneProc(Size amountNeeded)
+{
+  long    freedMem = 0;
+  
+  if (sMemoryReserve && *sMemoryReserve && sMemoryReserve != ::GZSaveHnd())
+  {
+    freedMem = ::GetHandleSize(sMemoryReserve);
+    ::EmptyHandle(sMemoryReserve);
+  }
+  
+  return freedMem;
+}
+
diff --git a/widget/src/mac/nsToolkit.h b/widget/src/mac/nsToolkit.h
index 075d7433cc3b..cf4691cc6613 100644
--- a/widget/src/mac/nsToolkit.h
+++ b/widget/src/mac/nsToolkit.h
@@ -101,5 +101,40 @@ protected:
 };
 
 
+// class for low memory detection and handling
+class nsMacMemoryCushion : public Repeater
+{
+public:
+
+  enum {
+    kMemoryReserveSize      = 32 * 1024   // 32k memory reserve    
+  };
+  
+                nsMacMemoryCushion();
+                ~nsMacMemoryCushion();
+                
+  OSErr         Init(Size reserveSize);
+
+
+  void          RepeatAction(const EventRecord &aMacEvent);
+
+protected:
+
+                // allocate or recover the memory reserve. Returns true on success
+  Boolean       RecoverMemoryReserve(Size reserveSize);
+
+public:
+
+  static pascal long  GrowZoneProc(Size amountNeeded);
+  
+  
+protected:
+
+  static Handle  sMemoryReserve;
+
+};
+
+
+
 
 #endif  // TOOLKIT_H