Mozilla has released version 3.01 of Firefox to fix these security issues:

http://www.mozilla.org/security/known-vulnerabilities/firefox30.html#firefox3.0.1

Update pushes should be happening already, and the download page has been updated too:

http://www.mozilla-europe.org/en/firefox/

Note this update disables some add-ons (notably TabMixPlus) that were marked as 3.0 compatible instead of 3.0.*