Most browser add-ons are created by a software developer to suit a particular purpose. There are hundreds of them, so generally you'll find one to perform the task you require. Problem is that they are often bundled with all sorts of other caveats. It's very difficult to develop your own Firefox add-on as this requires specialist skills and you need to read up on how to follow the strict APIs or your add-on may be disabled in a future browser update.27 May 2009