Ubuntu ships Firefox updates independent of its normal release schedule, so you should always have the latest version there, shortly after the official Firefox

Ubuntu ships Firefox updates independent of its normal release schedule, so you should always have the latest version there, shortly after the official Firefox release. But you might want to consider a different distro with more up-to-date packages anyways. It'll be consistently tested with those more up-to-date packages, so would most likely be more stable than your attempt to rejuvenate Ubuntu LTS or whatever distro you're using exactly.