The McAfee Site Advisor 3.3.1 extension was the number 2 cause of crashes in one of the Firefox 5.0 betas and Mozilla Blocklisted it. That extension is disabled in Firefox 5, Firefox 6.0beta, and Firefox 7.0alpha versions. McAfee is working on a new re-written version of the Site Advisor extension to fix their problems - ETA is mid to end of July.
https://bugzilla.mozilla.org/show_bug.cgi?id=660111

credit to the-edmeister

James, Thank you so much for your reply. I really appreciate it!! Definitely was very helpful.