Hi
Fedora 15 includes Firefox 4 by default
http://downloadsquad.switched.com/2011/04/07/first-firefox-6-build-next-w...
"Mozilla's Engineering Project Manager, Christian Legnitto, has detailed
the release schedule for Firefox 5, 6 and 7. If all goes to plan,
Firefox 6.0a1 will be released next week, April 12, and Firefox 7.0a1 in
the middle of May. The final build of Firefox 5 should be released on
June 21, exactly three months after the release of Firefox 4."
Rahul