So here's how to build a proper 64 bit firefox 19 on debian testing:
sudo apt-get install bzip2 build-essential python zip unzip pkg-config libgtk2.0-dev gconf2 libdbus-1-dev libdbus-glib-1-dev yasm libasound2-dev libcurl4-gnutls-dev libxt-dev mesa-common-dev mkdir ~/tmp/firefox -p cd ~/tmp/firefox wget ftp://ftp.mozilla.org/pub/firefox/releases/19.0.2/source/firefox-19.0.2.source.tar.bz2 rm mozilla-release -rf tar xvf firefox-19.0.2.source.tar.bz2 mkdir buildfirefox19/ cd buildfirefox19/ ../mozilla-release/./configure --prefix=$HOME/.firefox19 make make install echo "alias firefox19='$HOME/.firefox19/bin/firefox'" >> $HOME/.bashrc source $HOME/.bashrc
Start by running firefox19 from the terminal.