Much as it pains me to disagree, Firefox is not the most reliable download manager for resuming large DLs. On OS X and Windows, I find that more often than not it restarts from the beginning. On OS X, I trust downloads to Safari, which does resume reliably from most servers. On Windows, I tend towards IE. It's the same issue with which browser you'd use to ftp into a server that requires username/password in the URL: Firefox will show you empty folders and Safari/IE actually connect to the servers enough to authenticate, as does Konqueror in Linux. Some things are, sadly, managed best by the tools written specifically for their target platform by the OS vendors. If there's something I'm overlooking in Firefox, please, someone correct me.