So where do you go? I've installed one and clicked through all of my menus and can't find it anywhere. It's not in my OS launcher either.
If you install the app from its detail page, there is a message telling you where the app now lives. The "Free" install button becomes a "Launch" button that opens the actual executable.
On the search results pages, we don't add any messaging. I've filed an enhancement bug to consider exposing this to users: https://bugzilla.mozilla.org/show_bug.cgi?id=913728
edit: filed a bug