Aqua Mozilla Theme: Theme for mozilla 1.5, 1.6, and trunk.
CatThief's "Mostly Crystal" themes: Themes for Mozilla, Firefox, and Thunderbird running on Windows, Linux, and Mac OS X.
ICQ Quick Button for Mozilla: Allows you to start ICQ from a Mozilla toolbar icon.
Lopburi Flat Theme: The Lopburi Flat theme for Mozilla browsers.
Mozilla Modern Theme in PNG: The Mozilla modern theme converted to png format.
Mozilla Theme Afterglow: Colourful theme featuring Mozilla.org's mascot.
Mozilla Update :: Themes: Mozilla's official download site for Firefox and Thunderbird themes.
MozThemes: A collection of themes for Mozilla, Netscape, Mozilla Firefox, and Mozilla Thunderbird created by Aaron Spuler.
Pinball & GrayModern Mozilla Themes: Official home of the Pinball & GreyModern space-saving themes for Mozilla.
Sailfish-maintained Mozilla Themes: Contains links to many Mozilla and Netscape themes and other free internet stuff.
themes.mozdev.org: List of mozilla themes, info and a Theme Installer add-on.