Unfortunately, that growth has tapered off dramatically in the last couple of years. For comparison, in 2007 the Mozilla Foundation reported $75 million in revenue, a 12% increase over 2006. Mozilla chairperson Mitchell Baker goes into much greater depth on her blog, if you are interested.
Dollars aside, Mozilla's Firefox has steadily climbed to the world's second most used Web browser, chipping away at Microsoft's Internet Explorer. Firefox currently holds approximately one quarter of the global market share, and recently surpassed IE6, the most used version of Internet Explorer.
In somewhat related news, a rumor sprouted today which suggests that Sony may have plans to use Firefox on its PlayStation 3 console. The move is surely welcomed by most, as the PS3's built-in browser is considered to be less reliable and accurate at handling websites than a desktop-grade browser.