Please check Problematic Extensions a fix for McAfee Site Advisor is expected about third week in July, 2011. It hasn't worked all that well since Firefox 3.6

• McAfee Communities: Latest firefox update and Site Advisor...
  https://community.mcafee.com/message/195191#195191
• Problematic extensions - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Problematic_extensions

For those that really need an earlier version of Firefox, find your system and the Firefox version you want in releases, download and start the install.

• ftp://ftp.mozilla.org/pub/firefox/releases/

When reinstalling Firefox from a download, Firefox must be down once the installation starts. When the installation finishes, don't let the install start firefox for you. Instead end the install and start Firefox in your normal manner, thus preventing creating a new profile which does not have your bookmarks cookies, etc (but your old profile would still be around and would).

Thanks for the info. I guess I need to delay my updates or McAfee needs to stay ahead of Mozilla.

dmcritchie has given a very concise summary of the current position. Turnaround time to rewrite and test (thoroughly, I would hope) the SA plugin is going to be about 4 weeks. Sorry, but McAfee need to get it right or everyone's going to complain (again). I'll keep tabs on what's going on, and the issue will be raised in the weekly conference calls . If there's anything new to report I'll post something in one of the current SiteAdvisor threads.

What a disappointment. One of the reasons I downloaded 5.0 was because it was supposed to be more secure than 4.0. Now I find out that it won't run McAfee Site Advisor. My on-line hobby is entering contests which takes me to many unfamiliar websites and I've come to rely on McAfee Site Advisor as a tool to avoid going to questionable sites. You would think that Mozilla would have held off releasing 5.0 until this widely-used McAfee security tool was made compatible. Oh well, I guess I can go back to using Internet Explorer for my contest surfing until they get this resolved. Bummer.

It was not as it it was a secret that 5.0 was coming and McAfee has been aware of their toolbar causing crashing for pretty close to a month now in a early 5.0 Beta as they were notified back on May 27.

Thanks for the reply. I would appreciate any posting regarding McAfee updating their plugin.

https://community.mcafee.com/thread/36733?tstart=0

This above discussion was started recently about their toolbar extension only because Firefox 5.0 was only just officially released June 21.

McAfee has already had almost a month now to work on fixing their extension.

The following link is to a similar thread, the last post of which indicates SiteAdvisor now works with FF5. Haven't tested whether it is true, though.

http://support.mozilla.com/en-US/questions/837950

In addition to Web of Trust (have never tried it) you could also install AVG Link Scanner, which is similar to McAfee Site Advisor. I have both of those running on my PC. AVG Link Scanner also works on Safari on a Mac. Unless you have K-9 Web Protection installed, in which case it won't work.

I don't know if K-9 conflicts with AVG Link Scanner on a PC, though...

You certainly don't want anything to do with AVG Link Scanner, "AVG Safe" is the extension that it installs see Problematic Extensions.