ubuntu install any version of Firefox

https://ftp.mozilla.org/pub/firefox/releases/

1.sudo gedit /usr/share/applications/firefox.desktop

 

2. Set Desktop shortcuts

Exec = executable file directory address

Icon = icon Address

[Desktop Entry]
Name=firefox
Comment=firefox
Exec=/opt/firefox/firefox
Icon=/opt/firefox/browser/icons/mozicon128.png
Terminal=false
Type=Application
Categories=Application;
Encoding=UTF-8
StartupNotify=true