Now Finally firefox 13 is released for Ubuntu 12.04 with Speed Dial and Performance changes.Major Changes:1. Finally Speed Dial is here2.  Tab Performance is better3. Home screen change, now it includes shortcuts of  frequent used options .How to download Firefox 13 in Ubuntu 12.04 :Don’t need to do anything special it is available at Update Manager . You can update your firefox with using update manager.
Speed Dial :
New Home Screen :