Thanks. I had hoped for either some correlation with my history.log, or something connected to drawing/rendering the desktop, but nothing jumps out from those, alas. The nvidia/libnvidia-* ones from the 23rd would be the obvious suspect, except you had already posted about the problems (above) when those packages were getting installed.

The apparmor denials for Firefox seem to be a known issue. I don’t use Firefox (and back when I did, I used the Mozilla PPA version instead of the snap), but I suspect they’re not related to the freeze. At least not unless you’re running particularly low on memory.