hello omarcat, some other affected users tied the issue to the mcafee site advisor extension - please try to disable or remove that in case you have it present.

http://service.mcafee.com/faqdocument.aspx?id=TS100162

I read that some people think it's a virus.

no worries, it's nothing malicious, but it is caused by this one addon which appears to have compatibility issues with firefox 34...

I called McAfee and they are unaware of this problem.

See also these SUMO threads:

• [/questions/1034427]
• [/questions/1027393]

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I disabled the add-on, restarted Firefox. I enabled the add-on, restarted Firefox. Now everything is ok. I didn't have to uninstall the add-on.

Thank you for your help.

I disabled my site advisor and the problem is gone