waterfox from home:bgstack15 project

For Debian Unstable run the following:

Keep in mind that the owner of the key may distribute updates, packages and repositories that your system will trust (more information).

echo 'deb http://download.opensuse.org/repositories/home:/bgstack15/Debian_Unstable/ /' | sudo tee /etc/apt/sources.list.d/home:bgstack15.list
curl -fsSL https://download.opensuse.org/repositories/home:bgstack15/Debian_Unstable/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_bgstack15.gpg > /dev/null
sudo apt update
sudo apt install waterfox