Interesting! Didn't realize Ubuntu had included it already. I almost always assumed Ubuntu package manager is always behind by a few versions (like it is for everything else).

Ubuntu tends to keep Firefox up to date, although I haven't used Ubuntu for a few months already.

But regardless, this is the "official PPA" for the Beta channel: https://launchpad.net/~mozillateam/+archive/ubuntu/firefox-n...

for firefox there is really not any other way, because security updates are not backported. So either you have (ubuntu, ...) to pick latest or ancient ESR.