What do you mean they never responded? They say they are working on a response[0]. Taking time to respond and informing the other party that it will take a while is not "never responded".
3 months is a long time.... how long is someone supposed to wait for a response before you just move ahead? If the answer is "forever", it becomes trivial to perform a denial of service attack on a standard. Mozilla specifically said, "this is not high priority for us". If it's not high priority for them to respond, that's fine, but waiting forever doesn't seem like a reasonable thing to require.
[0] https://github.com/mozilla/standards-positions/issues/29#iss...