Fixed share link on Safari and better FF support

Added check for Mozilla, enabling use of both FF’s WebRTC impl. as well
as running OWR in FF. Switched STUN server.
nit: you could do:
`var isMozilla = window.mozRTCPeerConnection && !window.webkitRTCPeerConnection`
right away, test on that value, and skip the last assignment in the if-block.