User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36
Steps to reproduce:
Navigate to https://www.vektor.space/webudprtt.html on Firefox 64.0.2 (64-bit).
ICE-lite negotiation completes successfully, as evidenced by about:webrtc, but the channel fails to open.
In my own, alternate minimal implementation of an ICE-lite WebRTC Data Channel server, I see the connection fail during SSL negotiation; SSL_read eventually returns SSL_ERROR_ZERO_RETURN, signifying that the remote end (Firefox) closed the SSL connection.
Compare the results to Chrome or Safari, or an older Firefox build to see how it should behave. Essentially, the data channel should open once the ICE-lite negotiation completes, and there should be data exchange.