Firefox 3 introduced tighter OS integrating across all platforms, and even different Strata (Windows theme) flavors for Windows XP and Vista. However the result was not optimal and there is room to make Firefox feel more native.
Start with Glasser, an extension developed by Matthew Holder that adds Aero translucency to the whole Firefox toolbar area and not just the title bar. Strangely, after 5 months and 128 reviews averaging 5/5 starts it is still labeled as experimental, so you will need a Mozilla Add-ons account.
Second, you can make the bookmarks toolbar look like regular Vista toolbars with a glossy blue effect. If you’re using Stylish, just install this user style, otherwise copy the code and paste it in your userChrome.css file (located in your profile folder).
Third, tabs and group boxes look out of place in Vista. Note the border below tabs and the incorrect background color in the group boxes titles in the screenshot below.
This style will make them look as they should:
Finally, you can remove the menu bar installing Compact Menu 2, by Millie C. After restarting, right click on a toolbar and select Customize… Add the Compact Menu button somewhere in the navigation toolbar and press Done.
Right click again on a toolbar and uncheck the Menubar to hide it. You can still access all menu actions via the Compact Menu button.
Here’s how it looks in the end.