Web lists-archives.com

You cannot downgrade Firefox 55 profiles

"In short: If you want to switch to ESR, it may be a good time to do so before the Firefox 55 release. You may alternatively create a backup of the Firefox profile before you upgrade to Firefox 55, and restore it after you install Firefox ESR on your system.

Mozilla notes that the organization changed the "on-disk format of persistent storage in profiles" in Firefox 55, and that this change is the reason why you cannot downgrade to an earlier version of Firefox after you used the profile on Firefox 55 or newer."

general mailing list