Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

It turned out that the McAfee Site Adviser extension was the problem. The last one I would have guessed. Thanks.

Yep Site Advisor was the problem for me too.

Alright, so here is the problem. The newest version of Firefox is Beta (Firefox 4.0). Unfortunately, SiteAdvisor does not work with this version, but they will be releasing an update, but I don't know when that will be.

Obviously, you want SiteAdvisor to work since it is warning you about potentially harmful sites, so here is the fix.

THE FIX: You must uninstall firefox and re-install version 3.6.16. Also, you may need to uninstall and re-install SiteAdvisor (this is necessary if site ratings are showing in Yahoo, but not other search engines like Google).

If you are using McAfee Internet Protection for Mac you may need to uninstall and re-install it as well. Again, this is necessary if site ratings are showing in Yahoo, but not other search engines like Google.

Hope this helps!!

The MacAfee Site Advisor extension was the problem for me also. I have disabled it and the error message does not appear.