On: The 'Fuck You' Pattern

[commoner]

Is there an announcement, help page, or issue/commit explaining this feature?

[greenshackle2 → commoner]

There's this:

https://www.mozilla.org/en-CA/firefox/facebookcontainer/

I'm not sure if it's built into some versions now?

It does it on my Windows computer but not my Linux laptop, and I don't remember explicitly installing this extension on either.