> I often end up having to hold down the power button for 5 seconds.

If you enable the magic SysRq key, Alt+Print Screen+F will trigger the OOM killer.

Quick enable for those who want it:

  kernel.sysrq = 1

in /etc/sysctl.d/90-sysrq.conf.

> I blame most of it on Chromium and Firefox

I rarely have this problem with modern Firefox, but also block ads so maybe that makes the difference. Chrome is always bad, though.