Maybe you can find something in the logs
journalctl -qb /usr/bin/firefox
Hubert Hauser via arch-general email@example.com schrieb am Do., 20. Sep. 2018, 18:21:
I have problem with randomly crashing Firefox 62.0 or single tabs in this browser on 64-bit Arch Linux system. Running Firefox in safe mode doesn't help. Resetting browser or removing folder ~/.mozilla still doesn't help. Any ideas how to fix this issue?
Cheers, Hubert Hauser.