From Mozilla:

Mozilla has just announced Extend Firefox 3, their contest for developers to create new and interesting add-ons for the upcoming release of Firefox 3. Open now and running through July 4th, this contest awards entries that demonstrate excellence in user experience, innovativeness, and use of open standards.

New to this year’s contest, Mozilla will be announcing a special category to award prizes to existing Firefox Add-ons that update themselves for Firefox 3, and in particular, for developers who take the opportunity to improve the user experience and performance of their add-on.

Companies like del.icio.us and StumbleUpon have built their businesses as add-ons for Firefox – with exposure to more than 160 million users worldwide, a useful tool can become a successful business by building on top of the Firefox platform. 

You can find out more details at: http://www.extendfirefox.com/, and to see a list of Extend Firefox 2 winners go to: http://blog.mozilla.com/extendfirefox/.