There is a form here for reporting issues: http://community.mcafee.com/showthread.php?t=217274
Sorry if I sounded dismissive, but McAfee like almost every other software manufacturer I know of, does not guarantee anything when 3rd party beta products are involved and will not provide support for any issues arising from the use thereof. That's been their policy since time immemorial.
I'm sure that they are working on compatibility with any updates to supported browsers, such as Firefox 3 beta and IE 8 beta.
It's hit and miss if any siteadvisor engineer looks in here, especially at the weekend.