Two more download manager back-end changes landed recently. First, Bug 382825 added a potentially useful method:
void retryDownload(in unsigned long aID);
This will retry a download with the specified id, and fails if it cannot find the download in the database or if the download is currently in progress.
Then Bug 382839 landed, which enables
getDownload to return both active downloads and any download that is in the database. Extension authors will not have to directly query the database to get the information they need about the download.
I think this is probably about it for back-end changes for Firefox 3. Still fixing a few random regressions that have popped up, and an interesting leak was found, but otherwise, it is about time to move onto the UI overhaul!