We need to get very accurate values for the end-to-end latency (for the AEC), so I want to compare what we have inside gecko with the real latency, and see if we're missing something.

For this we can measure externally, but we have no way of quickly exposing audio input latency to get numbers from users, I'd like something in about:support.

It will require opening a duplex stream for a few seconds, and will only work for the default input device, I assume.

This has been fixed a while back, I must have filed it twice.