Though Firefox 3 introduced greater blending with OS themes, the blending is not upto what it should be. Mozilla Links blog has a nice article on how to blend Firefox in Vista Looks using various add-ons like Glasser to make Toolbar area translucent just like title bar, Compact Menu to convert menu bar into a single button and some user styles to give Bookmarks bar a glossy effect just like standard toolbar in Windows Vista Explorer.

Here’s the comparison of looks before and after applying those tweaks.