This extension sends HTTP HEAD requests to check the status of links. When you press the 'StartTrek' button, the extension obtains an array-like structure containing all the anchor tags (commonly called links). Using this array-like structure, the extension sends a HEAD-type request for each link and uses the response from the server hosting that page/resource to highlight the page. In the process, no information is sent to the extension developer, but information may be sent to the server hosting the link/web-resource. This information is same as the information which would be sent if you manually clicked each link on the page.