This would allow me to remove the devices in case a friend logged in at a hotel, or extraneous house. This could also help me troubleshoot with them if they needed to update their version.
Unfortunately, this is not an option; instead, it uses the name of the machine from which it is connected. Put this in a feature request, and maybe they’ll implement it in 12 to 54 years.
They belong to you, because every device you are seeing here has been connected to your account.
Unless of course you gave out your plex.tv credentials to your friends – which you should never do.
If you share your media “properly” with other plex.tv accounts, these have their own list of devices. Their devices don’t appear among your devices.
But considering that the majority of the items in the screenshot above are web browsers, I think there is something else going on:
Your web browser is deleting its cookies when you close it.
(either that, or you have some kind of “privacy enhancer” software which deletes them from your browser[s])
Now if you open the web browser next time, it has forgotten everything about plex.tv. A clear sign of that indeed happening is if you have to log into plex.tv each time you open your web browser fresh.
So, TL;DR: tell your web browser to not delete the cookies from the domain plex.tv.