Two recently released text-to-speech extensions can transform Firefox into a talking Web browser suitable for users with visual impairments -- and anyone else who can use a speech interface to the Web. Fire Vox is designed to be a full-fledged "screen reader in a browser," usable for daily browsing even for unsighted users. CLiCk, Speak provides point-and-click screen reading, which can be helpful for partially-sighted users or sighted users who have written language difficulties (such as dyslexia).
Both extensions are cross-platform, working with Linux, Windows, and Mac OS X. Separate instructions outline the installation steps for the different platforms, as the extensions take advantage of the different accessibility frameworks in the operating systems. On Linux, you can use the Java FreeTTS speech engine supplied by the project, or use the Orca accessibility framework provided by GNOME.