force-kills like sudo reboot will show UI on restart indicating it didn't shut down cleanly, but that isn't reported as a crash. You can see how often you actually crash via about:crashes (and also see what happened)
You should look at about:crashes and see if there's any commonality in the causes, or bugs associated with them (though often bugs won't be associated with the crash if it isn't filed from crash-stats or have the crash signature in the bug)
Google is deciding who are the winners on the web that get better performance (and surprise, google is chief among them, such as the youtube player) - with a very weak justification about why this penalty for security/privacy is worth it (basically "we allow 3PC tracking already, so this can't be worse than that")
I'm down to 7800 tabs (30 windows) on my main desktop. 4K on my other, 2K on my laptops. High was >11000 tabs. Firefox makes this easy; takes ~30 seconds to open all those windows and load a tab per window (plus ~8 pinned tabs)
"% string" in the awesome bar completes against tabs only. Helps a ton, along with some about:config settings that open new tabs from pinned tabs at the right (end) of the tab list. Also windows for separate contexts (though tab groups may also work here now, and avoid the overhead of opening a window/loading a tab at startup).
And "About Tabs" extension from glandium (who works for mozilla)
Many Firefox devs are on Linux; however note that not many Firefox users are on Linux (mostly because desktop Linux has a much much smaller userbase than Windows or Mac). About 4% are Linux, looks like 8-10% Mac, the rest Windows:
https://data.firefox.com/dashboard/hardware