Firefox 4 is available on FTP-servers Mozilla. Servers that publish files, can not cope with the load, so try to shove the user to other versions of the browser.

But "Mirrors" invented without reason, so if you can not wait to upgrade to the "Quartet", no one hurt to do it. A copy of the browser can be found on these sites: for systems Windows, Mac and Linux.

Before the upgrade, take into account the fact that the new browser does not earn all of your favorite plug-ins. Give them a week to developers second, that they have released their latest version.