Out of the box, only mp4 files are supported by firefly. Officially, video is not supported in firefly at all.
However, (kind of a coincidence), last week I tried to get video to work. Although my target was a bit different: I wanted to stream to the browser.
Not sure whether this might help you, but I’ll explain anyway. 🙂
The flash player in the browser only supports .flv and .mp4 files. Therefore, other video types wil be transcoded to .flv on-the-fly on request.
http://wiki.fireflymediaserver.org/Transcoding_HOWTO
This article explains on what transcoding is, how it works, and how to do it yourself.
If you’re interested in my transcoding script, let me know.