diff -up firefox-31.3.0/mozilla-esr31/extensions/auth/nsAuthSambaNTLM.cpp.old firefox-31.3.0/mozilla-esr31/extensions/auth/nsAuthSambaNTLM.cpp
--- firefox-31.3.0/mozilla-esr31/extensions/auth/nsAuthSambaNTLM.cpp.old	2014-11-25 12:23:22.000000000 +0100
+++ firefox-31.3.0/mozilla-esr31/extensions/auth/nsAuthSambaNTLM.cpp	2014-12-23 15:26:36.606674625 +0100
@@ -174,7 +174,7 @@ nsAuthSambaNTLM::SpawnNTLMAuthHelper()
         return NS_ERROR_FAILURE;
 
     const char* const args[] = {
-        "ntlm_auth",
+        "/usr/bin/ntlm_auth",
         "--helper-protocol", "ntlmssp-client-1",
         "--use-cached-creds",
         "--username", username,