This is similar to this issue: https://support.mozilla.org/en-US/questions/990487?esab=a&as=aaq After some period of use (hours and sometimes days), Firefox will suddenly stop displaying File Open and File Save dialogs. If I click a Browse... button to upload a file, there is a brief flash and nothing happens. If I am downloading a file that needs a destination path specified the download just fails (I don't get a File Save dialog). Closing and re-opening Firefox resolves the issue temporarily. I am still able to drag files onto the Browse button and attach that way, so the issue seems to be explicitly with the File Open and File Save dialogs refusing to open. I have at least 3 other users at my firm having the same issue. There *might* be a correlation with RDP sessions (i.e. if we connect to our workstations via RDP, when we later log in at the physical machine, the problem seems to happen. I'll need to test this a few times to say for sure. I started having this issue 6 to 9 months ago, so whatever it is, it's been happening for awhile.