Did you reuse existing profiles on both versions, or in either case did you start a completely fresh profile? If you haven't yet tested with a newly-created pro

Did you reuse existing profiles on both versions, or in either case did you start a completely fresh profile? If you haven't yet tested with a newly-created profile (which doesn't require deleting your existing profile), then you need to do so in order to triage whether the problem is with Firefox-by-default or Firefox-and-your-profile.