This is a Google-chrome extension to assist users of Codechef. It tick marks the questions that the user has solved (submitted and accepted).
To install the extension in Google-chrome, download the Codechef-assistant.crx file and drag-and-drop on an open instance of Google-Chrome. Chrome will ask for permission, authenticate to proceed with the installation.
For the 'doubtful', the source code is right in front of you ;)
Or simply download it from Google Chrome Webstore
A GreaseMonkey script for the same can be found here