Firefox is crashing many time a day on every page on Ubuntu 18.04 ...It is to the point of being unusable...
Do you have the same issue with Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf
Try downloading Firefox from Mozilla, run it from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release
Also, have you tried strace before?