problem with Firefox 36.01 update

Hi all,

This morning i updated from Firefox 36 to 36.01.

During the update a "File Insight" message from Norton popped up .

I never noted the exact words but it said that

Auto Protect is processing a security risk -

Then said it had quarantined "program files\Mozilla Firefox\Updated\Xul.dll" because it was infected with "Suspicious.Cloud.9.B"

I tried to start Firefox but it showed a message that the run file was missing.

I restored the Xul.dll from quarantine to the Mozilla folder and did a Mawarebytes scan. that was ok.

Tried Firefox again and it started and seems to be working ok so far

Is this a false positive?

Has anyone else experienced it?

Any advice or info would be much appreciated.

                                                                                            Norton 360 21.6.0.32  - Windows xp sp3