keybindings – Remap double keypress to key combo based on application in Karabiner?

I’d like to remap a double press of the fn key to map to a certain key combination based on the application in focus, for instance ⌘+/ in Atom, ⌥⌘+→ in Firefox, and ⌘Shift+D in iTerm? I’m guessing this should be fairly simple for anyone with much experience with Karabiner, but I can’t seem to find any good tutorials.