One thing I dislike about Firefox 3 is that the specialized themes for Windows XP and Vista both leave you with a Back button that is out of proportion with the other buttons on the toolbar. You can tame the oversized button by following this Tech-Recipe.
1. Open Firefox 3.
2. Right-click on the toolbar and select Customize.
3. Check the Use Small Icons checkbox, located at the bottom of the window.
The Back button is now in proportion with the other buttons, and no longer looks out of place.