nsIExternalProtocolService in Firefox 3.5

 Check whether a handler for a specific protocol exists.  Specifically,
 this looks to see whether there are any known possible application handlers
 in either the nsIHandlerService datastore or registered with the OS.

 @param aProtocolScheme The scheme from a url: http, ftp, mailto, etc.

 @return true if we have a handler and false otherwise.

 XXX shouldn't aProtocolScheme be an ACString like nsIURI::scheme?

 Gets a human-readable description for the application responsible for
 handling a specific protocol.

 @param aScheme The scheme to look up. For example, "mms".

 @throw NS_ERROR_NOT_IMPLEMENTED
        If getting descriptions for protocol helpers is not supported
 @throw NS_ERROR_NOT_AVAILABLE
        If no protocol helper exists for this scheme, or if it is not
        possible to get a description for it.

 Retrieve the handler for the given protocol.  If neither the application
 nor the OS knows about a handler for the protocol, the object this method
 returns will represent a default handler for unknown content.
 
 @param aProtocolScheme the scheme from a URL: http, ftp, mailto, etc.
 
 Note: aProtocolScheme should not include a trailing colon, which is part
 of the URI syntax, not part of the scheme itself (i.e. pass "mailto" not
 "mailto:").
 
 @return the handler, if any; otherwise a default handler

 Given a scheme, looks up the protocol info from the OS.  This should be
 overridden by each OS's implementation.

 @param aScheme The protocol scheme we are looking for.
 @param aFound  Was an OS default handler for this scheme found?
 @return An nsIHanderInfo for the protocol.

 Check whether a handler for a specific protocol is "exposed" as a visible
 feature of the current application.

 An exposed protocol handler is one that can be used in all contexts.  A
 non-exposed protocol handler is one that can only be used internally by the
 application.  For example, a non-exposed protocol would not be loaded by the
 application in response to a link click or a X-remote openURL command.
 Instead, it would be deferred to the system's external protocol handler.
 XXX shouldn't aProtocolScheme be an ACString like nsIURI::scheme?

 Used to load a URI via an external application. Might prompt the user for
 permission to load the external application.

 @param aURI
        The URI to load

 @param aWindowContext 
        The window to parent the dialog against, and, if a web handler
        is chosen, it is loaded in this window as well.  This parameter
        may be ultimately passed nsIURILoader.openURI in the case of a
        web handler, and aWindowContext is null or not present, web
        handlers will fail.  We need to do better than that; bug 394483
        filed in order to track.
 
 @note  Embedders that do not expose the http protocol should not currently
        use web-based protocol handlers, as handoff won't work correctly
        (bug 394479).  

 Used to load a url via an external protocol handler (if one exists)

 @param aURL The url to load
 @deprecated Use LoadURI instead (See Bug 389565 for removal)

 
 Set some sane defaults for a protocol handler object.
 
 @param aHandlerInfo      nsIHandlerInfo object, as returned by 
                          getProtocolHandlerInfoFromOS
 @param aOSHandlerExists  was the object above created for an extant
                          OS default handler?  This is generally the
                          value of the aFound out param from
                          getProtocolHandlerInfoFromOS.