Being a very limited user, I've never bothered to constantly update my iMac OS - Mail, and occasional shopping works perfectly. But recently I've found a problem with one of the two chess sites I visit. While lichess works as well as ever, Chess.com only works in a limited way - oddly, I can do puzzles, get the page for setting up a game with one of the bots - but the "play" button isn't "live." I even tried switching (reluctantly) from my default browser (Firefox) to Google Chrome. This works - up to a point. It seems that I can't update Chrome (which Chess.com out of nowhere now demand) which needs OS 10.11 - my iMac is 10.10.5. So I seem to be stuck. Is there any way out of this impasse? I've no outstanding updates, so it may be that I've got the most advanced OS I'm ever going to have.