Per this post on Stack Overflow: http://stackoverflow.com/questions/30848114/show-firefox-os-devtools-on-firefox-developer-edition-desktop The user has a ZTE Open C running 184.108.40.206-prerelease with Gecko 34.0 on the beta update channel. He reports that he intermittently can't see browser tabs in the WebIDE: "it works on Firefox v.38.0.5!! But it doesn't work on Firefox Developer Edition v.40.0a2. Actually, it works on Firefox Developer Edition, but only from time to time..."
When the remote connection fails there will probably be error messages either in the desktop Firefox Browser Console or in "adb logcat" from the device. We need these to have a chance at understanding what is going on.
I posted a comment on SO to ask about Browser Console logs.
No reply to my SO comment. I don't think we can really proceed here without active communication with the user, so closing for now. Please reopen if the situation changes.