Usually, changing your Firefox browser’s looks requires a CSS tweak, an about:config switch, or specialized downloads.
Stratiform is an all-in-one add-on that offers a variety of button, toolbar, and other visual element switches. Try out new themes and switch back without any hassle.
As Stratiform’s developer notes, these kind of tweaks required developer-level or deep-down changes before Firefox 4. With the latest release, add-ons like Stratiform make tweaking colors, dimensions, fonts, and other elements is pretty simple. Click what you like, and the changes take effect instantly, with no harm to anything.
Stratiform is a free download for Firefox on Windows only, and requires Firefox 4 or later.