I've recently had about 30 tabs open, both in Firefox and Firefox-ESR, on Debian Testing. After over 10 years on Debian, my system has begun to freeze somewhat

I've recently had about 30 tabs open, both in Firefox and Firefox-ESR, on Debian Testing. After over 10 years on Debian, my system has begun to freeze somewhat dependably and predictably when either browser has more than 5 active* tabs. Sometimes, but mostly not, I'm able to Ctrl/Alt/Backspace to kill X and then resume with startx. If I can do this, I'm able to rescue my session without a hard reboot. More often I must hard power down. And when Ctrl/Alt/Backspace does work it's after at least 20 attempts. I tried reducing the priority of FF, but not sure if it'll help. Anyway, as a compulsive tab horder, this is a completely new bug for me. But I will never give up, and if necessary I will fight to the bitter end. *Active as opposed to merely open Edit: maybe if Ubuntu releases Tabular Tyrannosaurus I'll change distros.