Mozilla Problem

Hey...

I downloaded Firefox, and it was fine as my default browser for a week or so, but then it started getting weird. Now whenever I open a link from email (Outlook XP) or any other source than a webpage, it opens IE (a blank page) and then opens Firefox with the correct page. I removed IE as the default, and set Firefox as default, which worked. I went into Program Access and Defaults, and under Custom (which I use), selected Firefox. I hit apply, and OK...and it locks up. Any suggestions? Thanks.