Although Firefox 3 looks better in Vista with different theme for Windows XP and Vista, there are still changes which can be made to Firefox, so make it look better in Vista. These changes can make Firefox have the look and feel of Vista. Glasser, an Firefox extension developed by Matthew Holder adds Aero translucency to the complete Firefox toolbar area and not like the default theme which gives the aero only to the title bar.
Another change which can be made to Firefox is to Install Stylish Add-on and add this user script to change the bookmark bar. With this user script, the bookmark toolbar will resemble the Vista toolbar.
The Glasser Firefox add-on is an experimental one, so you will need to login to download the add-on.
Thanks Mozilla Links