Unfortunately, Firefox still has failed to add the option to resume downloads. I've ran into this problem SO MANY times, and in my previous searches I found posts saying Firefox was going to fix that. As of 3.6.3 they haven't.
I just tried Free Download Manager (FDM), again, having the Firefox addon Flashgot use it. The download gets passed to FDM, and fails, giving the error message "access denied, invalid username or password." No password was required. The site I'm trying to get the file from is turbobit.net, which limits downloads speeds to 100kb/sec, and has a 59 second countdown before you get the link. I guess it's transparently using a password on their end. If I just download normally (save to disk) the download starts fine, but it fails after 30 minutes to 1 hour (always different), and my Wi-fi connection will stop briefly - and I have to start all over. So I will never be able to download a large file. I also tried DTA instead of FMD with Flashgot, and I get an "access denied" message in DTA. Again, I reloaded - waited the 59 seconds, and download w/Firefox, and the download starts fine. The failure message in the Firefox Downloads window is "source file at http... could not be read."
Any help would be greatly appreciated. When is Firefox going to finally add the ability to resume downloads????? Is there some other software I haven't found using Google that will work?