I should have said I disabled all my addons and ff works fine. as soon as I activate flash, it slows.

Several other users have reported a similar problem, which was getting repeated dialogs about a problem with an unnamed plugin. I don't think we found a solution, but in some cases, it was resolved spontaneously.

Since some of them also were Trend Micro security software users, could you make sure your program and pattern files are up-to-date in case this is a detection issue?

I do use Trend Micro, I'll try disabling it and using Defender and see if that works and I'll post back later. almost martini time so it probably won't be today! thanks for the quick reply.

The computer I was complaining about is at our cabin: I disabled TrendMicro and none of the addons are enabled and it seems to work better. My computer at home has the same FF, TrendMicro is enabled, and all addons are disabled. FF works more or less OK, could be a problem with internet speed (I use Century Link, 12 mbps but rarely even that fast) . So on one computer it is really really slow with trendmicro but on the other it doesn't seem to make any difference. I think I need to think about this more and do more troubleshooting before anybody else spends a lot of time helping me! Thanks!