Update --

I rebooted my machine, even though I had just done that when I noticed the problem. Dexpot is now back in the right-click title bar menu, and all of the actions are in the Dexpot menu below that, but neither Move nor Close have any effect. The window stays open on all desktops no matter what I do.

Dexpot no longer recognizes Waterfox. I can't move Waterfox windows between desktops. There's no Dexpot entry when I right-click on the Waterfox title bar. All other programs are still responding properly.

I'm running Windows 10 Version 1903 (OS Build 18362.239). Waterfox is version 56.2.13 (64-bit). I'm on a Dell Precision desktop.

Earlier today, Dell's updating program (I can't remember what it's called) had me install four updates. At least one was for audio, and one for USB, but I don't remember any more than that, and I don't know how to find out just what it did.

The Waterfox problem was present after the Dell update, but I don't know whether it might have been present before that.

Thanks for any help you can provide.