Mozilla.org has released the Firefox Roadmap 2. And it says "Firefox 2 will be based on continued development of the Gecko 1.8 branch created for Firefox 1.5. The goal is that Firefox 1.5 and 2 are compatible from a web developer's point of view." Firefox 2 final release is expected around late Q2 /early Q3 2006.
Firefox 2 Feature List Brainstorming is the place for feature planning and discussion in the Mozilla Wiki. It aims to create a single index that lists what sorts of things people are thinking of doing, with links to more detailed ideas about implementation specifics or concerns.
Ben Goodger, who is the lead engineer for Mozilla Firefox and runs the Inside Firefox blog reveals more features and -
"From a development point of view, the idea of Firefox 2 is to deliver significant user experience enhancements on top of a relatively stable rendering engine as significant retooling is done on the main development trunk for what will become Firefox 3, and deliver them in a timely fashion. By being deliberately cautious with our goals for the rendering engine, we hope to avoid long cycles of shake and bake that delayed Firefox 1.5 (which had more substantial Gecko changes than user interface changes)."