I will use Firefox today and see if it happens to me. My MacOS is a version newer than yours, but I can use the same version of Firefox. We haven't had other reports of this, but that doesn't mean others aren't having the problem.

I use Firefox and it happened right before I sent that message, and had happened more than once that day.

When is the last time this happened? There were some malicious ads that were causing some users' browsers to redirect them to an ad, but I think I fixed that earlier today. Your problem might have been related.

What browser are you using?

Not sure how to describe it, but only while on DCUM, my screen will freeze, then flicker/shake and I have to force quit. Is this something other people are experiencing? It's been going on for a few days now.