This is for anyone wanting to run Waterfox on Ubuntu 18.04. Open Terminal and run these commands.
#1 Make sure curl is installed by running ( sudo apt-get install curl )
#2 Update the sources.list ( echo "deb https://dl.bintray.com/hawkeye116477/waterfox-deb release main" | sudo tee -a /etc/apt/sources.list )
#3 Add the key ( curl https://bintray.com/user/downloadSubjectPublicKey?username=hawkeye116477 | sudo apt-key add - )
#4 Run the update ( sudo apt-get update && sudo apt-get install waterfox )

If Ubuntu is not up to date then the libgcc1 libstdc++6 package will have to be installed. If everything goes well then type waterfox in the terminal to open waterfox. You can also go applications and search for waterfox and then right click on the icon and pin it to the favorite bar.

https://askubuntu.com/questions/935466/how-do-i-install-waterfox
This link will help if you get lost.

Be advised Waterfox will only run on a 64bit OS.