Simpler than j127's solution is to download the last beta on https://download.mozilla.org/?product=firefox-beta-latest-ssl&os=linux64&lang=en-US, copy your profile into a new folder, then launch the executable with `MOZ_ALLOW_DOWNGRADE=1 /home/baptiste/firefox/firefox -P`, create a profile and choose the copied folder. All works smoothly and it takes 5mn.
Simpler than j127's solution is to download the last beta on https:/ /download. mozilla. org/?product= firefox- beta-latest- ssl&os= linux64& lang=en- US, copy your profile into a new folder, then launch the executable with `MOZ_ALLOW_ DOWNGRADE= 1 /home/baptiste/ firefox/ firefox -P`, create a profile and choose the copied folder. All works smoothly and it takes 5mn.