In Firefox, you can set up which external apps handle video files in the Tools->Options->Applications menu. It may be possible to create a popup menu directing the browser to play a video file with a particular media player using javascript. Adding javascript to a dirhtml script is easy, but overcoming default file type handlers may be difficult.
As an alternative to creating html files, you might try another program of mine, M3U Dropper, which creates playlists. It allows the user to select the media player to use.
http://home.comcast.net/~enitzsche/m3u_dropper/