diff --git a/mozilla/netwerk/base/src/nsIOService.cpp b/mozilla/netwerk/base/src/nsIOService.cpp
index e6089975ff6..86d4e4f767a 100644
--- a/mozilla/netwerk/base/src/nsIOService.cpp
+++ b/mozilla/netwerk/base/src/nsIOService.cpp
@@ -415,12 +415,26 @@ nsIOService::GetProtocolHandler(const char* scheme, nsIProtocolHandler* *result)
     rv = GetCachedProtocolHandler(scheme, result);
     if (NS_SUCCEEDED(rv)) return NS_OK;
 
-    nsCAutoString contractID(NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX);
-    contractID += scheme;
-    ToLowerCase(contractID);
+    PRBool externalProtocol = PR_FALSE;
+    nsCOMPtr<nsIPrefBranch> prefBranch;
+    GetPrefBranch(getter_AddRefs(prefBranch));
+    if (prefBranch) {
+        nsCAutoString externalProtocolPref("network.protocol-handler.external.");
+        externalProtocolPref += scheme;
+        rv = prefBranch->GetBoolPref(externalProtocolPref.get(), &externalProtocol);
+        if (NS_FAILED(rv))
+            externalProtocol = PR_FALSE;
+    }
 
-    rv = CallGetService(contractID.get(), result);
-    if (NS_FAILED(rv)) 
+    if (!externalProtocol) {
+        nsCAutoString contractID(NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX);
+        contractID += scheme;
+        ToLowerCase(contractID);
+
+        rv = CallGetService(contractID.get(), result);
+    }
+    
+    if (externalProtocol || NS_FAILED(rv)) 
     {
       // okay we don't have a protocol handler to handle this url type, so use the default protocol handler.
       // this will cause urls to get dispatched out to the OS ('cause we can't do anything with them) when