Ctrl+Shift+M Rated 5 out of 5 stars
Works great, but I can't find a way, not even in about:config, to turn off the association with Ctrl+Shift+M (which I prefer to bring up Firefox's built-in Responsive Design View). Double clicking on the Cookie Monster icon in the Add-on bar is sufficient accessibility to Cookie Monster's functionality for me. I don't want that repeated with an un-turn-off-able Ctrl+Shift+M association. So I hope the developer can change this.This review is for a previous version of the add-on (18.104.22.168-signed).