Comment 93 for bug 18995

(In reply to comment #15)
> the use-case of opening a file could be:
> (default -but rules could be specified by user to overpass the default
> association)
> automatically use the preferred user's application using xdg-open.
> IF NO preferred association found
> THEN popup dialog to the user like this
> http://www.amsn-project.net/w/upload/a/ab/Screenshot-4-5.jpg
> giving him the choice between manual path or a list of available application
> (using freedesktop standard specification)
> ..my two cents..

Fx already supports this and an app picker dialog, we just need to figure out how to populate it by implementing possibleLocalHandlers. (See bug 348808)