User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:76.0) Gecko/20100101 Firefox/76.0

Steps to reproduce:

0. Set up a multi-monitor desktop (e.g. mine has 6 monitors)
1. Configure system with multiple virtual desktops
2. Create multiple firefox windows. Arrange these to different virtual desktops, and to different screens within each desktop. Note the placements.
3. Power cycle (or reboot) host machine
4. Restart firefox
5. Review which screens of which virtual desktops that the windows are restored to.

A recent improvement (bug #372650) enables FF to restore windows to the virtual desktop they had been on.

A further refinement would be for FF to also remember which screen they had been on.

Actual results:

The windows get distributed to different virtual desktops, but not on the correct screens. I believe they're getting placed on Screen #0.

Expected results:

The windows should appear on the screen they had been on.

A recent improvement (bug #372650) enables FF to restore windows to the virtual desktop they had been on. This didn't use to work at all, so reboots were always an exercise in manually moving FF windows back to where they belong. This is an improvement, but still takes manual work to move windows to the correct screen.

Admittedly, this could well be a limitation of the window manager, however native Gtk apps are restoring properly so I'm guessing there's a way to make it work.

OS: Ubuntu 20.04
FF: 76.0 (64-bit) standard Ubuntu package
Window Manager: XFCE4 v4.14

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

I'm pretty sure there's a duplicate bug for this one, but can't find it atm :/