The Mozilla Toolkit is a set of APIs, built on top of Gecko, which provide advanced services to XUL applications. These services include Profile Management, Chrome Registration, Browsing History, Extension and Theme Management, Application Update Service, and Safe Mode. (More info)
While the video is buffering, hovering over the speaker gives me the volume control. After it starts playing, hovering doesn't produce the volume control, though clicking still mutes/unmutes.
It works fine if I load the .ogv directly.