http://kb.mozillazine.org/Problematic_extensions
http://news.softpedia.com/news/Mozilla-Mulls-McAfee-Site-Advisor-Firefox-Add-on-Block-253722.shtml
Mozilla Announces Fix for Firefox Memory Leak Caused by McAfee Add-On
No blacklisting was needed for McAfee's SiteAdvisor, this time
Mozilla is providing an update on the McAfee Firefox add-on that was found to cause serious issues. At the time, some Mozilla contributors argued that the add-on should be blocked/blacklisted until the problem was fixed.
http://www.siteadvisor.com/howitworks/index.html
if you got Firefox MyWOT works good