I've been able to reproduce it 100% of the times if I have 2 xul windows in different workspaces, either 2 firefox windows, or firefox and thunderbird. Changing to each with the Scale plugin will trigger this bug. It doesn't happen if both windows are moved to the same workspace.
I've been able to reproduce it 100% of the times if I have 2 xul windows in different workspaces, either 2 firefox windows, or firefox and thunderbird. Changing to each with the Scale plugin will trigger this bug. It doesn't happen if both windows are moved to the same workspace.