User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.3a5) Gecko/20100610 MozillaDeveloperPreview/3.7a5 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.3a5) Gecko/20100610 MozillaDeveloperPreview/3.7a5 On the most simple page with <audio> element first playback works without glitches. On second playback <audio> element resizes (doubles) vertically. It doesn´t matter, if element is for first time initiated by autoplay or by user. Reproducible: Always Steps to Reproduce: 1.Open page with <audio controls="controls"> element. 2.Hear it for the first time (using autoplay or click) 3.Click the play button. Actual Results: Audio element resizes. Expected Results: Audio element should not resize . Sometimes bug appear also while fiddling with "position in song" slider

That's a known regression.