I’ve figured out what the problem was. Turns out it was an extension that I’d missed .
Going with your suggestion, I temporarily disabled my security software. This caused some of my web connections to report errors, but for a brief moment W2G had started to work! Of course the moment I went to check another room, everything broke again.
I then wondered if maybe flushing my DNS would do something. It didn’t, so I downloaded Chrome and found that it did get W2G to work. But not wanting to give up on Opera I went back and retraced my steps, and that was when I saw that there was an extra browser extension that I’d missed.
Pop up blocker for Chrome™ - Poper Blocker, was screwing things up. It’s version 126.96.36.199, the version was deployed this morning. I’d added it to Opera several months ago, and forgotten all about it after hiding it from my browser’s toolbar. So today when I tried to disable everything, this one extension was the only one i’d failed to turn off. I should have been more thorough!
It looks like simply whitelisting Watch2Gether.com solves the problem, but clearly something was done to the extension to cause errors with the site, and I think it may be the cause of some other troubles I’ve had today.
Thank you for replying so quickly!