Installing Firefox

Hello everybody, I use Linux every day but I am just a common user with a problem: on my Debian 9 run laptop I have Firefox 68.8 esr 64 bit, and so far I am unable to install a new version of Firefox, but non-esr. I have downloaded the tar file and run the usual commands tar xjf... but nothing happened, just like if I had done nothing. So I asked for help in a linux forum, and the guys there told me two things:I could download Firefox as snap package(first time I heard of it),with the link provided I downloaded Firefox , run the commands, but at a certain moment I got the news that the installation was impossible because "core 18" was missing. The other thing the guys told me was to install Firefox from flatpak, and it was almost the same story: after some minutes I got the message that Firefox could not be installed because it needed a more recent version of flatpak.
So, back to square one, I am stuck on Firefox esr but I would like to change to Firefox 71 or 72. Can someone help me? Thanks from foyle, the poor linux user.