1. Instead of using CSS to hide it by default, make the script to only add it (perhaps by document.write, or alternatively by adding text to an empty <div> or <span>) if Chrome is detected. (This way it will be compatible even if CSS is disabled (or not implemented).)
2. Instead of Firefox, mention something else such as Line Mode Browser (it has some features I had not seen in other web browsers, but which I think are good and would like to have), or some other uncommon one which doesn't have Google and Mozilla etc, or more than one.