Download Firefox from this page: https://www.mozilla.org/en-US/firefox/all/#product-desktop-release
Open a terminal and go to the folder where your download has been saved. For example:
cd ~/Downloads
Extract the contents of the downloaded file by typing:
tar xjf firefox-*.tar.bz2
The following commands must be executed as root, or preceded by sudo.
Move the uncompressed Firefox folder to /opt:
mv firefox /opt
Create a symlink to the Firefox executable:
ln -s /opt/firefox/firefox /usr/local/bin/firefox
Download a copy of the desktop file:
wget https://raw.githubusercontent.com/mozilla/sumo-kb/main/install-firefox-linux/firefox.desktop \ -P /usr/local/share/applications