Since I find the new Proton GUI a step backwards in usability, I plan to defer the inevitable as long as possible by moving to the ESR version (currently V78). # How long are ESR versions supported? # What is the ESR version release cycle? # I plan to try using the -allow-downgrade command line option when downgrading, but the articles "[[Install an older version of Firefox]]" and "[[Command line options]]" are a bit short on step-by-step instruction. What is the correct procedure / sequence? # I have serious misgivings that the result will be usable, given the large difference in version numbers. I have made a backup of my profile. Should I have problems with the downgraded profile, I will presumably have to create a new profile. How can I recover data from the backup profile and import it into the new profile? # I am using Firefox Sync and hope that it will relieve me of some of the pain associated with a new profile. I am not syncing History however, because I prefer to keep the histories of my separate Firefox installations on different devices separate. Is there another way to preserve the history from a particular installation? # If not, what can I expect from sequentially turning on history sync on my various Firefox installations? # Will all history be merged or will subsequent history lists overwrite earlier ones? Any further advice which might prevent me from screwing this up would be most welcome!