Longstanding Firefox Add-on's/Vista User Account Problem

Vista Home:

One of the User Accounts on this PC will not disable/enable/uninstall or change any of the add-on's in Firefox (now on 3.6, but this prob has been ongoing for a year to a year-and-a-half at least). I have no pronlem with the other UA's on this machine.

Could screen shot #2 be the problem, please? I no longer have/use AVG on this machine (at least it's not currently installed).

Thanks in advance...

 

This link is what I found about removing add-ons in Firefox. http://kb.mozillazine.org/Uninstalling_add-ons

That's all I can help you with Glenn. Sorry.

PS: Just found another link: http://support.mozilla.com/tiki-view_forum_thread.php?locale=fr&forumId=1&comments_parentId=59330

 

Thank you very much for your time & efforts - I will let you know how it goes - thanks again...