CreditCardNanny is a Web browser extension for Google Chrome and Mozilla Firefox that detects forms that otherwise look secure (with a proper and valid SSL certificate, encrypted, and seemingly safe to enter sensitive data such as credit card details) but actually then submit this form data in a cleartext email to the site administrators. This extension detects such forms and warns you of the possibility that sensitive information may be exposed in clear-text, putting you and your sensitive data at risk. You can test the extension by browsing to https://cc-nanny.appspot.com/test-secure-page, a dummy credit card form that uses a form emailer script, a very common pattern used on an alarmingly large number of Web sites.
ff3sudoku is an add-on that features an engine for playing Sudoku puzzles. It can generate random puzzles, but it also detects and imports Sudokus from several Web sites, including websudoku.com, sudokupuzz.com, sudoku.com.au, and others. There is also a stand-alone version working in Firefox 3+ and GoogleChrome.