diff --git a/mozilla/netwerk/base/public/nsICachingChannel.idl b/mozilla/netwerk/base/public/nsICachingChannel.idl
index 5644b09c4de..24ca955be86 100644
--- a/mozilla/netwerk/base/public/nsICachingChannel.idl
+++ b/mozilla/netwerk/base/public/nsICachingChannel.idl
@@ -93,6 +93,13 @@ interface nsICachingChannel : nsISupports
      * an error if cacheAsFile is false.
      */
     readonly attribute nsIFile cacheFile;
+
+    /**
+     * TRUE if this channel's data is being loaded from the cache.  This value
+     * is undefined before the channel fires its OnStartRequest notification
+     * and after the channel fires its OnStopRequest notification.
+     */
+    boolean isFromCache();
 };
 
 %{C++
diff --git a/mozilla/netwerk/protocol/http/src/nsHttpChannel.cpp b/mozilla/netwerk/protocol/http/src/nsHttpChannel.cpp
index edffbad1924..aeeefe6abc7 100644
--- a/mozilla/netwerk/protocol/http/src/nsHttpChannel.cpp
+++ b/mozilla/netwerk/protocol/http/src/nsHttpChannel.cpp
@@ -68,6 +68,7 @@ nsHttpChannel::nsHttpChannel()
     , mFromCacheOnly(PR_FALSE)
     , mCachedContentIsValid(PR_FALSE)
     , mResponseHeadersModified(PR_FALSE)
+    , mCanceled(PR_FALSE)
 {
     LOG(("Creating nsHttpChannel @%x\n", this));
 
@@ -1751,6 +1752,7 @@ NS_IMETHODIMP
 nsHttpChannel::Cancel(nsresult status)
 {
     LOG(("nsHttpChannel::Cancel [this=%x status=%x]\n", this, status));
+    mCanceled = PR_TRUE;
     mStatus = status;
     if (mTransaction)
         mTransaction->Cancel(status);
@@ -2387,8 +2389,14 @@ nsHttpChannel::OnStopRequest(nsIRequest *request, nsISupports *ctxt, nsresult st
         mListenerContext = 0;
     }
 
-    if (mCacheEntry)
-        CloseCacheEntry(status);
+    if (mCacheEntry) {
+        // we don't want to discard the cache entry if canceled and
+        // reading from the cache.
+        if (mCanceled && (request == mCacheReadRequest))
+            CloseCacheEntry(NS_OK);
+        else
+            CloseCacheEntry(status);
+    }
 
     if (mLoadGroup)
         mLoadGroup->RemoveRequest(this, nsnull, status);
@@ -2571,6 +2579,13 @@ nsHttpChannel::GetCacheFile(nsIFile **cacheFile)
     return mCacheEntry->GetFile(cacheFile);
 }
 
+NS_IMETHODIMP
+nsHttpChannel::IsFromCache(PRBool *value)
+{
+    *value = (mCacheReadRequest != nsnull);
+    return NS_OK;
+}
+
 //-----------------------------------------------------------------------------
 // nsHttpChannel::nsICacheListener
 //-----------------------------------------------------------------------------
diff --git a/mozilla/netwerk/protocol/http/src/nsHttpChannel.h b/mozilla/netwerk/protocol/http/src/nsHttpChannel.h
index ecf1286c6ab..6e260d68a8e 100644
--- a/mozilla/netwerk/protocol/http/src/nsHttpChannel.h
+++ b/mozilla/netwerk/protocol/http/src/nsHttpChannel.h
@@ -171,6 +171,7 @@ private:
     PRPackedBool                      mFromCacheOnly;
     PRPackedBool                      mCachedContentIsValid;
     PRPackedBool                      mResponseHeadersModified;
+    PRPackedBool                      mCanceled;
 };
 
 #endif // nsHttpChannel_h__