The numerous third-party extensions available for Firefox are created for a variety of reasons. In many cases, extensions are created by members of the open source community who might have a passion for a particular element that they think will help all Firefox users. Other extensions, such as the Mozilla Amazon Browser, are created as a "proof of concept" to showcase the power of XUL and what you can do to develop web applications with Mozilla. Other extensions are created to satisfy the needs of a particular target audience. A good example of such an extension is Biobar, a search toolbar for searching bioinformatics databases that also provides links to bioinformatics tools. In other instances, the popularity of sites such as Google has spawned a number of extensions that help optimize the Google search experience.