Javascript Facebook Login on mobile web don't work

I have found a ton of questions on this but no real answers. My Facebook login works perfectly on desktop, but fails on mobile browsers (tested on Chrome and Safari). With mobile Safari I get the pop-up which asks me to log in, but never get the window requesting permission for my app... and the redirect doesn't fire and user does not get logged into my map :(

I'm using pretty standard Facebook login flow/logic.

I have used http://ift.tt/PFY4fe before for a native app which worked, not sure if it'd work for this case but either way I would prefer to roll my own here.

Does anyone know how to make Facebook login via Javascript SDK work on mobile browsers?