I use Gentoo Linux under KDE desktop with alsa for sound on a laptop. Sound works ok. However, when I start Firefox, specifically Aurora 33.0, the latest version in Gentoo, the default open page has a nice video - the Choose Independent Choose Firefox video. I can play it, and it plays fine, but there is no sound. I can download this as a file called fe0d3698-5a38-40e9-bdbe-8a3d7a4d07d9.webm and play it fine (in Dragon Player) I can play it fine when I go to the Mozilla.org site, and it comes up before the main site home page can be seen. I've tried other WebM videos, with no issues. Flash sound works fine, e.g. in YouTube. This is not a major issue - it's just odd!