--- a/netwerk/cache/nsCacheService.cpp
+++ b/netwerk/cache/nsCacheService.cpp
@@ -1133,16 +1133,17 @@ NS_THREADSAFE_MEMORY_REPORTER_IMPLEMENT(
     "Memory used by the network memory cache.")
 
 NS_IMPL_THREADSAFE_ISUPPORTS1(nsCacheService, nsICacheService)
 
 nsCacheService::nsCacheService()
     : mLock("nsCacheService.mLock"),
       mCondVar(mLock, "nsCacheService.mCondVar"),
       mInitialized(false),
+      mClearingEntries(false),
       mEnableMemoryDevice(true),
       mEnableDiskDevice(true),
       mMemoryDevice(nsnull),
       mDiskDevice(nsnull),
       mOfflineDevice(nsnull),
       mTotalEntries(0),
       mCacheHits(0),
       mCacheMisses(0),
@@ -1887,17 +1888,19 @@ nsCacheService::OpenCacheEntry(nsCacheSe
 
 
 nsresult
 nsCacheService::ActivateEntry(nsCacheRequest * request, 
                               nsCacheEntry ** result,
                               nsCacheEntry ** doomedEntry)
 {
     CACHE_LOG_DEBUG(("Activate entry for request %p\n", request));
-    
+    if (!mInitialized || mClearingEntries)
+        return NS_ERROR_NOT_AVAILABLE;
+
     nsresult        rv = NS_OK;
 
     NS_ASSERTION(request != nsnull, "ActivateEntry called with no request");
     if (result) *result = nsnull;
     if (doomedEntry) *doomedEntry = nsnull;
     if ((!request) || (!result) || (!doomedEntry))
         return NS_ERROR_NULL_POINTER;
 
@@ -2169,16 +2172,17 @@ nsCacheService::OnProfileShutdown(bool c
 {
     if (!gService)  return;
     if (!gService->mInitialized) {
         // The cache service has been shut down, but someone is still holding
         // a reference to it. Ignore this call.
         return;
     }
     nsCacheServiceAutoLock lock;
+    gService->mClearingEntries = true;
 
     gService->DoomActiveEntries();
     gService->ClearDoomList();
 
     // Make sure to wait for any pending cache-operations before
     // proceeding with destructive actions (bug #620660)
     (void) SyncWithCacheIOThread();
 
@@ -2198,16 +2202,17 @@ nsCacheService::OnProfileShutdown(bool c
     }
     gService->mEnableOfflineDevice = false;
 
     if (gService->mMemoryDevice) {
         // clear memory cache
         gService->mMemoryDevice->EvictEntries(nsnull);
     }
 
+    gService->mClearingEntries = false;
 }
 
 
 void
 nsCacheService::OnProfileChanged()
 {
     if (!gService)  return;
 

--- a/netwerk/cache/nsCacheService.h
+++ b/netwerk/cache/nsCacheService.h
@@ -285,16 +285,17 @@ private:
     mozilla::CondVar                mCondVar;
 
     nsCOMPtr<nsIThread>             mCacheIOThread;
 
     nsTArray<nsISupports*>          mDoomedObjects;
     nsCOMPtr<nsITimer>              mSmartSizeTimer;
     
     bool                            mInitialized;
+    bool                            mClearingEntries;
     
     bool                            mEnableMemoryDevice;
     bool                            mEnableDiskDevice;
     bool                            mEnableOfflineDevice;
 
     nsMemoryCacheDevice *           mMemoryDevice;
     nsDiskCacheDevice *             mDiskDevice;
     nsOfflineCacheDevice *          mOfflineDevice;