One of the things that about:config helped me to fix in Firefox was stopping the browser from closing when I close a tab I’ve finished with - and it was the last one! Somehow this is so unnatural for me that when a browser is configured to close when last tab closes, I accidentally close the browser time and again. Very frustrating!
There’s an issue logged for this. I added your comment as +1 and you can track the progress here
sriram closed #3