I don't believe the number of tabs open has anything at all to do with my issue. I seldom have more than 2 or maybe 3 open at once. I have read that it's probably a conflict with my add-ons or virus software, but I'm not going to turn off either of those (that were not an issue before the "upgrade.")
There was an old post for a prior version that offered help: go to the firefox menu ≡ > options > privacy & security panel, under the permissions section enable the setting to prevent accessibility services from accessing your browser and restart once. But that path is invalid in the current version, and I could not find accessibility services anywhere on my machine. The only advice I've seen for the current version is a known compatibility issue with the Malwarebytes extension (this was on a WIN 11 machine.) I only have a DuckDuckGo privacy extension, a VideoDownload extension, and AdBlock. Other comments say that this version is a memory and CPU hog. I'm glad I got 8bg...but right now it's at 80%.
Apparently the Malwarebytes add-on (Malwarebytes Browser Guard) is also a problem on Win10. I disabled it earlier and that seems to have fixed the problem. I have been using that add-on for a few years, as well as regular Malwarebytes Premium so I guess their "upgrade" created a conflict.
Yes. And Firefox points users to Malwarebytes. We have seen reports from Firefox 113 users that Malwarebytes Browser Guard is causing slowness issues, so if you use this extension best is to contact its Malwarebytes for support. I use Malwarebytes Premium as well, but have not installed the Add-On (or the Extension, or whatever they call it.)