Debian by default comes with Iceweasel web browser instead of firefox. Although it is recommended to use Iceweasel you may have a need to install firefox are here is a simple way how to install firefox on Debian wheezy by using Linux mint's debian import repository.
This is a companion discussion topic for the original entry at https://linuxconfig.org/easy-way-to-install-firefox-browser-on-debian-7-wheezy