After a strange crash that I still can’t explain, I updated my video driver (nvidia) and could no longer function with Xinerama. Running 3 monitors with separate X screens is okay for my use for now – it is limited in that you can’t drag windows from one screen to another, but it also lets you swap workspaces in each screen individually.
I can handle not being able to drag windows between screens, but some applications really benefit from having different windows open – and they fall apart when you attempt to open separate windows in different screens. Firefox, and LibreOffice being top of my list.
Firefox works with separate profiles. Start the program with a -P once, define a new profile, and then you can have it prompt on startup each time. I may set up something like my LibreOffice fix later.