I experience this, usually a couple of times per day. For me, NVDA is too inactive to use Task Manager to see what process is seizing-up my laptop or tablet. I don't have a desktop shortcut to kill the Firefox process because I didn't know Firefox was to blame. Usually using the Alt+Shift+n shortcut to force NVDA to re-start will work and, as long as I use that brief moment of NVDA life to close a few programs that I figured might be responsible (Firefox and WinAmp and word) I can make sure that I have any unsaved documents saved before re-starting my computer.

I do use Chrome as well as Firefox, but since Firefox is still running with its tabs open when I also use Chrome, I don't know whether this happens if I'd only used Chrome that day. I much prefer the Firefox browser.

I'm using the latest Firefox (86.0) and the latest stable NVDA (2020.4) on both a Surface Pro 4 tablet and an Asus gaming laptop, both using Intel processors and 8Gb memory.

Giles
Giles