Oh... It IS working for me, which means it's either a browser caching issue, or you're using Brave.
Brave doesn't allow JavaScript's localStorage to be shared even between tabs on the same site - which means that several forum features including multi-quote won't work.
And there's no way to turn it off... so, I actually switched back to Firefox! That's a real show-stopper since localStorage is used for EVERYTHING these days, and there's no real good security reason that I can see to prevent multiple tabs on the same site from communicating with each other.