

Do you use the “Restore Previous Session” feature of your web browser between reboots? Do you use keyboard controls to open new windows like Ctrl+N?
If yes to both, chances are that your mystery window had remained part of that continued session, and was reactivated with a Ctrl+Shift+N or equivalent. Shift is right next to Ctrl so if you fat-fingered a Shift at the same time that could explain the apparent necromancy.
As to where it went originally, you could have moved it to a different virtual desktop, moved it off-screen accidentally or, heck, even misclicked or miskeyed to have it actually close. A reboot would then have closed it for certain, except for the fact that it was still lurking in your session.
Another thing that can cause windows to move around is when a HDMI or DisplayPort monitor disconnects. Unlike with older connection types, those disconnecting is detectable and modern window managers try to “save” windows by throwing them on any remaining active monitors. If you have both types of monitor connection, or had at some point in the past, it could be that your mysterious window was lurking on a screen you couldn’t see but the system still thought exists, at least until it was closed for certain.
Admittedly unlikely, but you could rule that out by checking the system monitor arrangements in the settings.



Binface could easily do better than Farage has. I mean, it’s not exactly a high bar.
Farage barely shows his face there and almost never in Parliament.
You can guarantee that Binface would be more than willing to show up in both places frequently. He might even go so far as to represent Clacton properly. Perish the thought!
(I can imagine that if he won they wouldn’t let him into the Commons due to not being dressed sensibly and then refusing to recognise him if he does so, because that’s the sort of dirty trickery I’d expect from Parliament. So I’d be very interested to see what he does in order to comply with both directives at the same time.)