I spend whole weekend to figure out why I am unable to run firefox 4 on my 64 bit machine..
Actually whenever I was downloading, I was getting 32 bit firefox.. The correct url for downloading firefox for 64 bit is
http://ftp.jaist.ac.jp/pub/mozilla.org/firefox/releases/4.0.1/linux-x86_64/en-US/firefox-4.0.1.tar.bz2 64 bit version too..
Firefox 5 beta
By- Narendra Sisodiya