Rtuk is an ironic tool that enables anonymous users to "censor" any text on any web page. Blacked out text is automatically stored in a central server, and a connection is made each time a user enters a page or enables the add-on, so that they see an updated, erased version of the Internet, shaped by all Rtuk users anonymously. It's an analogy of bottom-up censorship as well as a reference to the artistic tradition of erasure.
Rtuk can be enabled/disabled through the Status bar or the Tools menu. Selected text can be blacked out through the Context menu or the Rtuk button added to the toolbar.