I installed the addon again and SAVED the game. However, the next day I try to LOAD the game and get the error message that the addon is not there.
After much experimenting, I discovered that if I CLEAR CACHE in Chrome, the addon disappears. If I don't clear cache, the addon remains. It appears to me that the addon is treated like a COOKIE in Chrome. If you delete Cookies, you delete the addon. Is that how it's supposed to work?