Although there are no official Debian repositories for Waterfox, it can be installed from a repsoitory with APT.

Repository: opensuse.org

Therefore use this commands:

sudo apt update && sudo apt upgrade -y

sudo apt install software-properties-common apt-transport-https curl -y

Quick install:

Just run the following command to get the repository key and install it:

curl -fsSL https://download.opensuse.org/repositories/home:hawkeye116477:waterfox/xUbuntu_24.04/Release.key | sudo gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_hawkeye116477_waterfox.gpg > /dev/null

Then add the repository to the sources lists:

echo 'deb http://download.opensuse.org/repositories/home:/hawkeye116477:/waterfox/xUbuntu_24.04/ /' | sudo tee /etc/apt/sources.list.d/home:hawkeye116477:waterfox.list

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Longer, bit outdated way:

wget https://download.opensuse.org/repositories/home:hawkeye116477:waterfox/Debian_11/Release.key 

Replace Debian_11 with your distribution, e.g. Debian_12. Therefore have a look at download.opensuse.org/repositories

gpg --dearmor Release.key && cat Release.key.gpg | sudo tee /etc/apt/trusted.gpg.d/home_hawkeye116477_waterfox.gpg > /dev/null 

rm Release.key*

echo 'deb http://download.opensuse.org/repositories/home:/hawkeye116477:/waterfox/Debian_11/ /' | sudo tee /etc/apt/sources.list.d/home:hawkeye116477:waterfox.list

sudo apt update 

sudo apt install fonts-lyx ffmpeg -y waterfox-g-kde

Sourced from linuxcapable.com

Simply run:

flatpak install flathub net.waterfox.waterfox

Disclaimer: packages might be a bit outdated when sourcing from flathub!

When installing Waterfox on a KDE/Plasma environment, it could be that Waterfox's default setting is to use a custom title bar like this:

In some configurations this can look very ugly like above. But it's possible to change this, therefore navigate to More tools > Customize toolbar and tick the check in the lower left corner that says Title Bar:

Finally your Waterfox should look like this:

Sourced from askvg.de - Firefox Settings

It might be, that some webpages will be displayed in Times New Roman font, to fix that install the missing fonts by just installing the packages ttf-mscorefonts-installer and fonts-lyx:

sudo apt install ttf-mscorefonts-installer fonts-lyx ffmpeg

The package ffmpeg will additionally make video and audio output possible.