Chromium

Chromium is getting better. This long waited release is characterized by the inclusion of a very needed feature: support for extensions.

So, if you've missed some functionality/feature from Firefox, now you can install the equivalent in this browser. There are plenty of "ported" extensions for Firefox users (for example: Firebug Lite, Web developer, Gmail Notifier) as well as unique, new ones.
The installed extensions start working when opening new tabs, with no need to restart the browser (thanks to the separation of tabs in individual processes). Really awesome!

Another great feature is the support for visual themes. You can browse them in a gallery, see the preview and install them with a single click. The interface is user-friendly and intuitive, so it is very easy to add and remove themes.

The best thing of all is that Chromium is open source, and absolutely free. No contracts, no naggy updater programs on your PC. Just what you want: a great browser, extremely fast and customizable.