Yeah, a lot of our engineering effort is going into performance right now, rather than new features. But here are some of the HTML and CSS features in Firefox 4:

- HTML5 parser (SVG/MathML in HTML, new semantic elements)

- HTML5 forms (only partly implemented so far)

- Web Sockets

- CSS3 transitions

- CSS3 calc()

- IndexedDB (schemaless client-side database)

- WebM (VP8) codec for HTML5 video

- SVG backgrounds and images in CSS and HTML

- ECMAScript 5 features in JavaScript