Since Google Gears isn't supported on Firefox 4.0 us WebSQL developers have been left in the dark when it comes to Firefox support.
HTML5 WebSQL for Firefox is an add-on that provides exposure of basic WebSQL functions through a wrapper of some of the internal SQLite functions in Firefox.
More info about WebSQL and the HTML5 Web Database API at http://www.w3.org/TR/webdatabase/
Our first Firefox extension! Please contact us if you'd like additional functionality or have any bug reports.