Key links include:

Mozilla Firefox version 6 released
http://www.mozilla.com/en-US/firefox/new/

Mozilla Firefox version 6 support
http://support.mozilla.com/en-US/home

Mozilla Firefox version 6 new features
http://www.mozilla.com/en-US/firefox/features/

Mozilla Firefox version 6 security
http://www.mozilla.com/en-US/firefox/features/#advancedsecurity