Kempelton is a style of icons and a theme for Firefox which uses them. For various reasons (see blog post), the theme is no longer available for current versions of Firefox.
Kempelton was originally conceived when I was developing the updated graphics for Mozilla Thunderbird 2.0. I wanted an icon set that blended in with modern operating systems and still had its own character.
Here you can download zip files containing the icons, that may be used for example in web sites and software. They are available in the common PNG format as well as the original SVG vector format, in which you can easily edit or resize them.
Available under the Creative Commons Attribution-Share Alike License.
Mozilla Firefox Themes
There are two Kempelton themes, the standard one and a version with very large toolbar icons, called simply Kempelton Large. They are only available for the outdated Firefox 3.6, so I can’t recommend using them anymore.
Adaptations by Others
KDE icon theme by Schiwi