https://support.mozilla.com/en-US/kb/Firefox+crashes#Getting_the_most_accurate_help_with_your_Firefox_crash

Type about:crashes in the URL bar and hit Enter. Click the hyperlinks to bring up the Crash Report pages and copy'n'paste the URL of each of those reports into the message box here. We'll see if we can help you figure out what is causing those crashes to happen.

I've been having this problem a lot, here are the most recent crash reports that were listed when I followed the instructions from the-edmiester

https://crash-stats.mozilla.com/report/index/1f49857e-9c5f-49f4-b303-cb6312120409

https://crash-stats.mozilla.com/report/index/3b810e5b-4c83-4db8-b165-62ef32120404

https://crash-stats.mozilla.com/report/index/08cd9d2f-8c6d-4fc7-83fd-3382d2120402