When the player types save, returns error "failed to save game" I'm guessing this is a browser problem/setting, but don't know how to fix it.

Did you (or the player) login before playing?

I have a feeling this can happen if you have a script missing a quote or a curly brace or something. If the script runs whilst playing the game, you will get an error, but if it has not run, you will not see the error and not realise there is an issue. Quest seems only to check when saving a game, rather than when saving in the editor, when it would be useful. I could be wrong on that, though,