Take a look at this article: https://support.mozilla.com/en-US/kb/Unable%20to%20download%20or%20save%20files?s=firefox+won%27t+download&r=0&as=s I had this problem with MP3s, they would play directly and not download to my system. I looked in Tools/Options/Applications and found that MP3 files went directly to a QuickTime application. They would play immediately. I changed the setting for MP3s to "download." The bad (QuickTime) setting was changed by downloading FireFox8, I did not have it this way in the previous FireFox. You should also check other file formats that you want to download and make sure that the setting is "download." Otherwise they might just go ahead and play or crash and you wont be able to save the file.