It's a browser extension that marks transphobic users.
Last time I've heard of them is whem they released an update with undocumented changes and without the source code. They also didn't respond to users concerns.
The technology they use also has issues with occasional false positives.
That is when I uninstalled it. Although it has been a while and things might have gotten sorted out since then.
There was an update a while back that picked up my Green status on Twitter and applied it to my Mastodon account.
My status on Reddit is neutral because I'm mostly posting there about tech stuff.