Given how bad the current Github UI is (and how sloppy the rollout was) I'm quite content to attribute it to incompetence rather than malice, but:
Type a long blurb into a text input widget e.g. a comment on a pull request. The text just bounces up and down as you type. I've noticed this with whatever the extended support version of Firefox (macos 10.14) is and with the current Firefox (macos 14.1). To be fair GH renders widgets partially off screen with whatever version of Safari comes with macos 10.14 There is no more static text on GH so if you go back further than that (or have javascript disabled) nothing renders at all.
There's no issue tracker (because why would there be?) but there was a discussion thread. Last I saw someone posted detailed steps to reproduce a search bug and the GH response was to lock the discussion thread.