Firefox updates fail with norton antivirus

Every time Firefox tries to update Norton Antivirus kills it with this message

Category: Resolved Security Risks
Date & Time,Risk,Activity,Status,Recommended Action,Path - Filename
4/16/2015 2:38:54 PM,High,xul.dll (Suspicious.Cloud.9.B) detected by Auto-Protect,Removed,Resolved - No Action Required,c:\program files\mozilla firefox\updated\xul.dll


and I basically have to reinstall Firefox again. Fortunately I have an old copy of IE that can access the internet. This has happened with the last two updates on Firefox. Should I be telling Norton to ignore the xul.dll or what?