Although not officially, but Google Chrome does support Themes now, but if you want to stick with good old Firefox for now and don't want to miss the sleek Google Chrome theme, Give Chromifox a try.

Get a coat of Chrome on Firefox, a bright and soft blue theme for Firefox 3 on Windows, Linux, and Mac OS X, inspired by the theme from the Google Chrome web browser.

Information & Installation >>

As with all BETA add-ons for Mozilla product you will need to login before downloading this.