This is one of the more exciting new features — to me — in Firefox 3. It’s now possible for web sites to register themselves as handlers for protocols. For example, if you have a web mail service, it can register to handle “mailto” URLs, which is really an enormous convenience.
Although the DOM method registerProtocolHandler() has been documented for a while now, Mark Finkle has finally added to MDC a how-to guide for how to implement a web-based protocol handler.
If you have a web site that might benefit from implementing a web-based protocol handler, be sure to check this out!