download , decompress , double click the file named "firefox" in folder to run
that's all~

But Firefox does not install it, how can I install it so I can see it in the starter

create a desktop entry file like this:

[Desktop Entry]
Encoding=UTF-8
Name=Firefox
Name[en_US]=Firefox
Comment=Firefox
Exec=/path to firefox/firefox
Icon=/path to firefox/browser/icons/mozicon128.png
Terminal=false
Type=Application
Categories=Application;Network;

sava it as firefox.dektop, and copy it to ~/.local/share/applications
then you can find it in lancher

wget http://ftp.mozilla.org/pub/firefox/releases/57.0b13/linux-x86_64/en-US/firefox-57.0b13.tar.bz2
tar xf firefox-57.0b13.tar.bz2
sudo cp -rf firefox /usr/lib/