For a while, I have ignored the “browser incompatible” messages that appeared here, and on similar sites, until today, when I couldn’t log on anymore.
Since my regular Firefox browser, is up-to-date, I knew that wasn’t the problem. It was actually the Windows7 OS on this pc, which I have no intention of updating.
On this Reddit topic, found various alternatives, and went with r3dfox, a fork of Firefox.
So far, so good, but I haven’t tested it to see whether all the regular Firefox plugins I use are available.