Debian Linux comes with Firefox ESR (Extended Support Release) version, which in some rare scenarios may not adequately fit your needs. The objective is to replace the Debian's default Firefox ESR with the latest bleeding edge Firefox.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-install-latest-firefox-browser-on-debian-9-stretch-linux
OHPRG
Well thank you very much for completely wacking Firefox off my system…I shall now find a post that will walk me through the necessary steps to correct this and hopefully do it properly…
William Amaya
Great post!!
Tofawn
firefox has no update option in settings. How do i update firefox from firefox?
Randy Noseworthy
Worked like a champ. One DOES need to know when to use Sudo or SU or not.
victorklos The Mozzilla.debian dot net link does not update to the latest version of Firefox for Debian Stretch. - Others shouldn’t even bother going there.
rbrband No, leave the old install there. It doesn’t go horribly slow, and you want to use the old link as shown in this tutorial.
Lubos Rendek -> Randy Noseworthy
Check the conventions for # vs $ at the top of the article. Perhaps, this is getting too old school now! 
Randy Noseworthy -> Lubos Rendek
The article works. But why you chose to reply to my offhand comment vs answering the other real questions seems a bit odd.
Ketsa -> victorklos
the only version in that repo is 52 esr…
plmosqueda -> victorklos
not working for stable, only testing and unstable
GtaSaKompanion -> victorklos
This repo isn’t working.
rbrband
Don’t we have to uninstall Debian’s deprecated version of Firefox first? Otherwise, the work would be wiped by a glacially slow update, one day. I ended up without even an icon after I did that. I had to create a launcher, etc.–I had to start with the /opt/Firefox55 Firefox version I had previously set up in order to get to this info (and the Libre page) again: Even when the version 56 extract is installed, rebooting proves necessary. Before rebooting, Firefox indicated version 55, still. I noted that proved true before… Thanks!
rbrband
I like that this is simplified over the old info.
Don’t we have to uninstall Debian’s deprecated version of Firefox first? Otherwise it will overwrite this work as it updates that–glacially slowly over time. It’s been a long process–I’ve had to create a new launcher, etc. Given the updating and uninstalling, I had not even an icon. I used the version 55 from opt and worked from there…