I think you might have something that's a bit of a stumper. I'm sure all the experts have looked at it by now. I've actually been looking at it off and on for the past few days.
It's not quite the right shape to be an insulator. The glass color is right, but they're not usually round like that.
Does it have any grooves or threads like it could be held inside a fixture (sort of like a ceiling light globe)?
Hmm... It looks more like a fixture than a bowl, but without any marks where it was held, that's not likely. I'll keep looking to see if I can solve the mystery.