I have just switched the header communication for FirePHP from the X-FirePHP headers to the wildfire headers (
http://www.wildfirehq.org/).
The next evolution of the wildfire protocol will allow for two-way communication at which point there will be extra headers indicating what the client is capable of handling. You will be able to use these headers to determine availability of FirePHP (rather than the user-agent header).
I don't have a timeline yet other than "early next year".