Running 24/7 with often system suspension and standby with at least 3 windows open with approx 150 tabs in each window. since +60d without restart. Win10.

When you get a lockup when Firefox is running, check your network card drivers and your graphic card drivers. In my experience, locking of systems is caused by software accessing some faulty interfaces/drivers. I speak for Windows.

Oh yeah, I don't like updates for restarting reasons, so it's still the newest but not the latest version

Same here, been about a month. And it really locks up, though it does a good job of reopening all my tabs.

Very anecdotal but I’ve been experiencing random lockups and the only common thing I’ve noticed is that every time it happens, Firefox is open.

No haven't encountered any bugs or lock ups at all.

I had zero problems on Mac or Android

Yeah, me too. I just went back to Chrome.