brushfe
(Sorry to necropost; I was going to post this very question.)
I'm having the same issue in testing my multiplayer game. Latest Chrome connects to host and sends messages between hosts and peers consistently. Firefox will connect to host, but not send certain messages. Internet Explorer (Windows 7) doesn't connect to host at all.
Before filing a bug report I thought I'd ask if anyone here has any clues?
I just tested the built-in multiplayer example (ghost shooter) by first logging in via NW.js (Host) then via FireFox (as Peer) and it worked fine.
Can you provide a very minimal example that we can all test?