Is there a way to turn off that little pop up thing in the bottom right of the screen that pops up everytime a download is finished saying "all downloads are complete"? I find it very annoying. Thanks!

Yes there is. Type about:config in the address bar and hit enter. In the filter list of the about:config window enter the following:

browser.download.manager.showalertoncomplete

Right click the entry that comes up in the window and click toggle to change the value to false

Another way is via the options panel. Options -> downloads->advanced and make sure the "show alerts when all downloads are finisheded" is unticked

See the screenshoot:

That is only available if you have the Download Manager Tweak extension installed.

Thanks. I'd already looked in the options/downloads/advanced menus and couldn't find it. I'll do it the about:config way. Thanks again.