In some (not all) calls, audio latency will rise and run way behind video, on the order of seconds. Something must be buffering audio for a LONG time and getting confused about sync; I consider this separate from bug 785584, which looks at the system pipeline latencies (such as MediaStreamGraph and cubeb). This has been seen in calls even within one house (over wifi). It could be related to lost RTCP; bug 864654 fixes some causes of lost RTCP packets.
We too have experienced a significant latency with audio/video. We have a consistently reproducible example of this. If anyone wants to see a demo of this latency effect, please let me know and I will send you a URL and instructions to view this.
Dup of both bug 884365 and bug 886886 Lew's issue is a dup of bug 901527