If you installed Sezen - either the stand-alone app or the Applet, you definitely noticed the "Websites" option does not work - that's because you need a Firefox or Chrome extension.
I couldn't get the Firefox extension to work (update: for Firefox, see Vadim's comment - but if you're using the Mozilla Daily PPA, it will probably not work), but the Chrome extension is easy to set up. All you have to do is get the zeitgeist-dataproviders branch (of course, make sure you have Sezen with the libzeitgeist dependency installed first!):
sudo apt-get install bzr libzeitgeist-dev cd bzr branch lp:zeitgeist-dataproviders cd zeitgeist-dataproviders/ ./autogen.sh cd chrome/ make sudo make install
Alternatively you could use "make local-install" instead of "sudo make install" to use the extension in its current location instead of "/opt/google/chrome/resources/zeitgeist_plugin".
At this point the Chrome (I've tested it in the latest Chromium dev build but it should also work in Google Chrome) extension is ready. To use it, in Chrome type "chrome://extensions", enable the developer mode by pressing the "+" sign next to "Developer mode" in the right:
Then click on "Load unpacked extension" and browse for the "/opt/google/chrome/resources/zeitgeist_plugin":
That's it. Now restart Sezen (be it the separate application or the panel applet).
The Firefox extension is also available in the zeitgeist-dataproviders branch you've just downloaded but like I said, I couldn't get it to work. But you can try for yourself...