It could be related to Firefox's integration with Windows' security policies. You could try turning that off. This assumes you have real-time antivirus software that checks every download automatically when you save it to the hard drive. (If not, you should!) If so, try the following:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful. This is Firefox's about:config preferences editor.

(2) In the filter box, type or paste scan and pause while the list is filtered

(3) Double-click browser.download.manager.scanWhenDone to switch it from true to false. (One of the features of the scanWhenDone feature is that it marks the file as sourced from the internet, which triggers your IE security zone settings.)

Then go back to another tab and try a new download. Any change?

Before I try the above solution I thought I'd add that IE 9 doesn't work with a damn and freezes often while I have UAC enables also. Got any ideas as to what might cause both IE and FireFox to not like UAC?

I might also add that I was using Freedownloadmanager to download files and it stops in it's tracks when UAC is enabled. So I quit using it so I could trouble shoot the browsers.

I run Windows 7 with full privileges, and haven't noticed any unusual issues with UAC. I see prompts for software installers as expected, but otherwise, it seems to stay out of the way. Maybe I unknowingly disabled something.

Well Microsoft tech support was working on this damn thing last week and after he got done this is the problem he left me. After him ruining two OS's on two different hard drives, I'm not about to let them back on my pc.