Rated 5 out of 5 stars
Letely I've been having this issue where downloaded files get renamed from:
archive.tar.gz to archive_tar.gz
addon-1.2.3.xpi to addon-1.2_3.xpi
...so, it seems that the dot before the last one is sopmehow replaced by an underscore. I'm not suggesting that this addon is causing the issue, I'm simply reporting it because it could possibly provide a solution. It already allows tokens/dates to be added to the filename, so I'm throwing the idea on the table to also support regex file-renaming or extension-changing rules. How about it?