This is an old revision of the document!
So in Debian lets open a terminal and type:
(Note: If you have a firefox profile you have been using you will need to back that up or you will lose all your tabs/saved passwords etc if you dont make a copy first.)
sudo apt-get purge firefox-esr
You will note that if you read the output Debian must have a web browser installed as part of its apt requirements so it will suggest chromium instead of Firefox. We will accept this recommendation and just press y. We want a sandboxed version of Firefox for daily use and will keep chromium as a backup browser in case we need it.
Now we need to install snaps:
sudo apt-get autoremove sudo apt-get install snapd sudo apt-get install gnome-software-plugin-snap sudo systemctl list-unit-files | grep snap sudo systemctl start snapd.service sudo snap search firefox sudo snap info firefox sudo snap install firefox --channel=esr/stable sudo reboot
(Reboot is done or snap doesn't seem to initialize properly and add firefox to your list of apps in the activities menu. I did take a quick look for a service that needed started but wasn't able to see one really quickly so just moved on. Everything works as expected after the reboot anyway but feel free to poke around a bit more if you want to try avoid rebooting. Most likely something isn't initialized right after install of snapd.)
Firefox is now working as the ESR snap on Debian also :)
Notes: