Bizarrely, this appears to be missing from the main site...

Ah, I basically only use the Android app, and this is hidden under the button that one expects would launch the confusing and awful Android sharing dialog.

This is kinda useless. You can bookmark a tweet. But when you undo this bookmarking, all other bookmarked tweets also go.

I don't have this option on tweetdeck, only a add to collections, gives me a popup with no content. Nice.