Firefox can't handle large downloads.
Whenever I try to download a large file, the download stops partway through. There's no particular pattern to when it stops; sometimes it'll freeze up within the first minute or two, sometimes it'll get almost to the end before dying. In any case, the download speed for that download drops to zero, and won't pick back up under any circumstances, even though I still have full internet connectivity for general browsing and can even download smaller files no problem. It might have more to do with the filehosting services that provide these large downloads, but it happens for any large file, no matter where I'm download from. I've had it happen on Megaupload, Fileserve, Hotfile, Uploaded.to, Zomg Uploads, and a number of private file servers. If the server in question plays nice with Flashget I can use that, but I can't use Firefox's built-in download capabilities for anything larger than a few dozen MB.
Alla svar (2)
It is possible that your anti-virus software is corrupting the downloaded files or otherwise interfering with downloading files by Firefox.
You can try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.
See http://kb.mozillazine.org/Unable_to_save_or_download_files
Looks like that did the trick, thanks a bunch!