Whenever a website prompts for me to upload or download a file and I except Firefox crashes, quitting in its entirety. This still occurs in "Troubleshoot" mode so I assume it is not any of my extensions. [https://crash-stats.mozilla.org/report/index/df84d9b3-c3a0-4b1e-9bf4-90ba30221212 Here] is a crash report from when this occurred if it helps. Another odd observation I made is that I am able to upload a file if I use a "drag-and-drop" feature on a website.