This thing started popping up on my screen. What is it and how do I make it go away forever?

tanstaafl.

Is this inside your browser? Could be you've got a malware browser extension / plugin. Is it outside your browser? Could be some kind of native malware.

Do you use Steam? Is this what Steam chats look like? Could be some kind of Steam-related issue.

That’s Steam’s friend/chat list, and it seems they are auto popping it up to promote some new redesign of the voice chat option with a recent update.

Doug, here’s how to disable Steam from auto starting at boot:
Open Steam
Go to the Steam menu - Preferences
On the left pick Interface
Uncheck the option next to “Run Steam when my computer starts”

Easy for you to say. I stumbled around through the Steam website for the better part of half an hour before I finally discovered...

That seems to have done the trick. I had previously disabled the Steam in the Windows Startup menu, but to no avail.

tanstaafl.