This is sort of a two part question.
If I use my moll-e, or my ohuna perch mailbox, or cantrips book (nightborne mail), can other players see them and use them?
Second part of dumb question: When I use my special effects hearthstones (let’s say Necrolord) Can other players see my super cool green swirlies as I hearth out? Or am I just standing there doing an imaginary thing no one else can see?
yes to both. have fun!
no. my mailbox.
Thanks for the replies! I think I found my answer regarding the hearthstone effects. My graphic settings were too low so changed in the options panel. So since I never saw anyone else hearth out (they just fade out) I didn’t think anyone could see mine. Trivial but these are the important questions 
Regarding Moll-E, is it engineer-only? I have one that I drop when I’m out and about and can’t be bothered to head back to town, but I’m not sure if just anyone can use it.
It’d be a shame if it were restricted.
I think anyone from the same faction can use the moll-e, is what i found on google. I’ve started using these toys a lot more as the mailbox trot is so tedious. Hope other players can use them too!
It’s engineer only to drop.
But anyone can use it once dropped.
I tried dancing on Katy and she said NO! BAD BEAR! OFF OFF