This has to be one of the strangest issues I've seen.
With one user account, when I download a PDF with firefox, instead of opening Foxit like it is supposed to when opening it it just starts opening up tons of tabs.
I checked a hijack this log and nothing came up.
I installed FF3 (over FF2 which had the problem first).
I installed Foxit for pdfs (originally Adobe reader was used and was causing the issue).
If your confused, we originally had FF2 and Adobe Reader installed which gave us the same issue with opening up tons of tabs when downloading a file and selecting open with. Then I uninstalled Adobe Reader and installed Foxit and we had the same problem. Then I installed FF3 and we still have the same problem.
This only happens with 1 user account, the other two on the computer work fine.