Acrobat Reader opens all links in IE

Whenever I click on a link inside a PDF file it opens it in IE. Since my default browser is Firefox I would like all links to be opened in Firefox. This isn't much of a problem but it definitely is a nuisance.
I've tried looking though Acrobat's settings but I didn't find anything helpful and reinstalling Acrobat Reader didn't work either. :( Also, all the other apps I have perform ok, that is they use Firefox to open links.

Also important, I'm using version 5.0 and would rather not upgrade.

If anybody has any ideeas about what I could try next I would definitely welcome them. Thanks.