Unless it’s a RAM filling issue, because you would have too little RAM, and even then, the entire OS crashing and not just Firefox would be very unlikely, I don’t see any reason for it to crash your entire OS. Regardless, there are Firefox forks that use much much less RAM. You’re using Windows, Mac or Linux first? Try to uninstall, clean everything and reinstall with a new profile, it may work, who knows. If not, then it has to be your OS.