Hi,
The feature that you request is not really suited to a server application like Firefly that may well be running on devices without keyboard or screen. However, there are a number of remote control applications available that you may not be aware of. Take a look at these threads on the Roku forums…
http://forums.rokulabs.com/viewtopic.php?t=14539
http://forums.rokulabs.com/viewtopic.php?t=3904
http://forums.rokulabs.com/viewtopic.php?t=6800
http://forums.rokulabs.com/viewtopic.php?t=10006
Personally, I use the last one of these most often if I need a basic remote control, but it depends on what you like, what you need…