It used to be the case that I pored over Mozilla (and later Firefox) release notes. But I stopped sometime in 2004, around the point when I accepted that XUL development was too hard to be doing in my spare time and yes, Firefox was clearly better than IE at just about everything.
This means that I now miss all the cool announcements
http://webkit.org/specs/CSSVisualEffects/CSSTransforms.html
http://dev.w3.org/2006/webapi/selectors-api/#queryselector
http://www.dustindiaz.com/firefox-31-brings-good-stuff/