Greetings.

It has been some time now, if you have the latest version of McAfee it should work. If not as far as I know it disables only the site advisor for firefox the rest of the anti virus is working. Just get in the program and disable the site advisor so firefox would leave you alone.

Further answers to the question at :

https://support.mozilla.com/en-US/questions/848920

Cheers

RaZoR

The McAfee Site Advisor add-on for Firefox is the only thing that would be disabled, everything else related to McAfee should work just fine. Plus, you don't really need that extension at all, as it duplicates features that have been a part of Firefox for over 3 years now. http://www.mozilla.com/en-US/firefox/phishing-protection/

That add-on is blocklisted by Mozilla due to that Site Advisor extension being the #2 cause of crashing the Firefox 5.0 betas. McAfee was notified of the problem long before that extension was added to the blocklist. Now it is up to them to fix it, and they better be close to a solution as Firefox 6.0 will be released in another 10 days - I wonder if they're gonna be ready for that version, too.
https://addons.mozilla.org/en-US/firefox/blocked/
https://bugzilla.mozilla.org/show_bug.cgi?id=660111

My advice is to switch to a free AV application which doesn't install silly garbage like that Site Advisor to begin with and save your self the grief it brings with it.
Avira Personal Free - http://www.free-av.com/