I have to agree, Firefox's download manager is not reliable. I actually have to download my purchases from Renderosity with IE due to problems with Firefox dropping the connection or just hanging in the middle of the download. If you then pause and resume the download (in an attempt to get it to start downloading again), it just stops and says the download is complete, even though you've only got part of the file. It totally screws limited download sites like Renderosity.

If you don't like GetRight's nagging, Download Accelerator Plus can be used free if you can put up with a banner on the application window. It's not a big deal considering you can minimize the program. Just don't tell it to integrate itself with your browser otherwise it'll try to intercept every download and that's not good with sites like Renderosity. Just right click on the link and "Copy link location" to start the download.

Don't use it with Renderosity because download managers are not supported, and it'll screw your download count up without downloading anything.