LittleFox, designed for optimal screen usage, leaving lots of room for browsing. Includes support for many extensions.
Install the About Home Themer extension to also theme the about:home page.
This add-on allows one to customize the theme "Classic Compact". Options include: 10 different toolbar button sets; turning off gradient backgrounds; OS scrollbars; dark system color support; merging menu bar into one menu button; etc.
Mozilla 1 / Netscape 4 classic theme for Firefox and Thunderbird
Myfirefox is the theme of the most perfectly simulating Internet Explorer 8 by far.
It can work perfectly in Windows 7 .
Chromin Frame places the tab bar at the top of window, and replace the title bar and window frame bringing it closer to the Chrome look.
It's design to work with any theme.