Similar question to this thread:

http://groups.google.com/group/micro... 3c54c84006eaa

In my case, when clicking on a link in email (OL 2003), I want it to
open Firefox. I do have the extension associations set for FF, for
things like jpg, and several others. However, when the link is
something like http://thisdomain.com/wordpress - where there is no
extension, it's opening AOL. Can't uninstall that as it's my work
computer and homeowner uses AOL versus my using Outlook and the
broadband ISP's email.