Comment 7 for bug 245776

Thomas K - After looking at your link, I seem to recall seeing this issue once before when trying to download a PDF. I can't reproduce it though, but I found this link, which suggests deleting download history using Tools -> Clear Private Data when you experience problems downloading files:

http://kb.mozillazine.org/Unable_to_save_or_download_files

And already having an existing file with the same but owned by a different user in /tmp doesn't stop Firefox from downloading a file. I just tried it, and it just appends a '-1' on the end of the filename.