Latest Firefox download is here [ ftp link for download latest firefox ]

Download latest firefox and all firefox versions Click HERE

or

http://ftp.jaist.ac.jp/pub/mozilla.org/firefox/releases/

How to enable firefox button in firefox4

Right click on the Tab Bar and uncheck the Menu Bar Option 
if you using firefox 5 already it apply! 
[to hide  firefox menu  press F10]

See Firefox Button !! Have Fun :)