Have you upgraded to Firefox 3.5 yet? If so, you might want to get a theme for your firefox that fits to your current Windows 7 edition.
The default theme of firefox is not transparent and is a simple grey theme, pretty boring, right? One way to improve that would be to check out the latest firefox personas (for beta 3.6) or to get a new theme for 3.5.
If you are an advanced user, you should just go ahead, grab the beta and download some cool personas (brand-new firefox themes).
You will find all the links in this post: Firefox 3.6 Beta fully supports Windows 7
But if you want to stay away from buggy and unstable beta versions, you should take a glance at the following Windows 7 firefox theme: Firefox 3.5 Theme
You will need the firefox plugin “Glasser” for this theme to get that shiny effect. Download Firefox Glasser
Firefox 3.7 Windows 7 GUI
In the near future, firefox will revamp the GUI and change the contextual menu. Firefox will have a loading bar that will probably be integrated into the Windows 7 taskbar as well. Additionaly 3.7 will add a Zoom function to the contextual menu (right-click) that many people did not know about.
If you want to zoom in firefox, you can simply hold STRG and use your mouse wheel to zoom in and zoom out.