apt-get remove iceweasel

echo -e "\ndeb http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all main" | tee -a /etc/apt/sources.list > /dev/null

apt-key adv --recv-keys --keyserver keyserver.ubuntu.com C1289A29

apt-get update

apt-get install firefox-mozilla-build

https://forums.kali.org/showthread.php?647-switching-to-FireFox-on-Kali-made-simple