Rated 4 out of 5 stars

Nice and simple to use.
Too bad it's only Firefox shortcuts and not global hotkeys, but I guess you need a desktop app for it.

This review is for a previous version of the add-on ( 

With bit of work you could try to make shortcuts global. https://github.com/intarstudents/keySharky/wiki/api-server

Example for Window: http://intarstudents.lv/groovesharks-global-keyboard-shortcuts-in-windows/