The changes are a lot less than with the 3.6 to 4.0 jump, but this is mainly because they decided to greatly shorten their release schedule.
Download it here.
Changes:
Improved HTML 5 and CSS3 support
Improved overall performance
Firefox 5.0 Web apps
A Do-Not-Track option
Download it here.
Changes:
Improved HTML 5 and CSS3 support
Improved overall performance
Firefox 5.0 Web apps
A Do-Not-Track option