The Interclue extension is supposed to give you a preview of links in Firefox before you visit them, saving you mouse-clicks and, with a little luck, allowing you to move quickly between multiple links on the same page. Unfortunately, the determination to monetize the add-on and keep its source code closed results in elaborations that make the basic idea less effective, and its constant pleas for donations make Interclue into nagware. As much as the usefulness of the basic utility, Interclue serves as an object lesson of the difficulties that the decision to go proprietary can take.