diff -r 229683caa4c3 extensions/pref/system-pref/src/nsSystemPref.cpp
--- a/extensions/pref/system-pref/src/nsSystemPref.cpp	Sat Nov 08 08:35:54 2008 -0800
+++ b/extensions/pref/system-pref/src/nsSystemPref.cpp	Wed Nov 12 00:08:38 2008 -0400
@@ -302,6 +302,18 @@ nsSystemPref::ReadSystemPref(const char 
         mSysPrefService->GetCharPref(aPrefName, getter_Copies(strValue));
         SYSPREF_LOG(("system value is %s\n", strValue.get()));
 
+        // Usually frontend applications for proxy settings store the proxy value
+        // prefixed by its protocol. Mozilla does not like that so we cut the protocol
+        // part off before set that.
+        if (!nsCString(aPrefName).Equals("network.proxy.autoconfig_url")) {
+            if (StringBeginsWith(strValue, NS_LITERAL_CSTRING("http://")))
+                strValue.Cut(0, 7);
+            else if (StringBeginsWith(strValue, NS_LITERAL_CSTRING("https://")))
+                strValue.Cut(0, 8);
+            else if (StringBeginsWith(strValue, NS_LITERAL_CSTRING("ftp://")))
+                strValue.Cut(0, 6);
+        }
+
         prefBranch->SetCharPref(aPrefName, strValue.get());
         break;
     case nsIPrefBranch::PREF_INT: