Update! For the last day or so, the back arrow in my Opera has been working almost unfailingly on the first and occasionally the second click. So, what has caused this change? In addition to the Xenforo update, I have checked for Opera updates thru the Help toolbar and though there is none, the operation of checking silently updates Java use in Opera. Whatever the reason for the big improvement, if not total solution, if I don't come back you can assume the problem with Opera is no longer an issue.