It seems that FireFox leaves those partial download files if for any reason they get interrupted. It's possible to resume the download through various uninteresting means, but if you're like me, it gets filled up with files that I intentionally did not complete downloading. If you're terminal-savvy, you can set up a script that cleans up old .part files. Here's what I've set in my crontab: 0 * * * * /usr/bin/find ~/Downloads/*.part -atime +1 -exec rm {} \; &> /dev/null It will delete any files in my downloads folder that are at least 1 day old. To install this in your crontab, launch terminal and type "crontab -e" This will bring up a text editor, probably vi. You'll see a bunch of ~'s down the left side. Type "i" to go into "insert" mode. The bottom left will say "-- INSERT --" Copy and paste (or type) the line of code I have above. Hit enter just to make sure you have a newline at the end. Hit "Escape" to exit the insert mode. Hit Shift-Z Shift-Z (that's Shift-Z twice) to exit the editor. You should see a status message "crontab: installing new crontab" If you type "crontab -l" you should see your newly installed crontab. At the top of the next hour, any .part files that are more than a day old should be deleted, and this should continue forever.