I use the Panorama plugin with Firefox. It lets me set groups of tabs and switch between them without closing them. It’s a bit like having separate windows but

I use the Panorama plugin with Firefox. It lets me set groups of tabs and switch between them without closing them. It’s a bit like having separate windows but more controlled. I use a different group for each project I’m working on. In a given say I’m usually working on 5 project plus administrative tasks that get their own tab group.