I'm using Firefox 62.0.3 with Win10 x64. Every now and again, when attempting to attach a file in Gmail, or some user forum, Firefox just disappears. There's no warning of any sort, or any sort of error message, it just disappears. I've tried in vain to find some sort of error log. I can start it up OK, but sometimes I get a message saying there are problems with trying to restore the session, but it usually restores OK if requested. If I try the same attach I get the same result. If I do exactly the same thing in MS Edge, it works fine. Other times (most times in fact) it attaches files with no problem. I can find no clue as to the actual cause, and the problem has been occurring over several Firefox updates. I cannot reproduce it at will, but when it happens I can generally repeat the error by retrying the attach. When the problem is encountered I have successfully navigated to the folder containing the file I want to attach, but when I try to open the folder, Firefox disappears. Repeating the thing in MS Edge always works.