Great! Rated 5 out of 5 stars
Works just great.
My only real complaint is that although you can decide whether or not the icon will show up on the toolbar, address bar and status bar, you can't disable it from showing up in the (right-click) context menu. That's the one place I don't want to see it, because I already have plenty of addons that put something in the context menu and it gets really cluttered.
Here's just another improvement idea: How about right-clicking on the button in the address/tool/status bar to access the options and/or quickly change the shortening service?
Oh, and the scissors icon may not be the best idea - people associate it with “cutting” stuff rather than copying. (Okay, I may be overgeneralizing. :) )