Hey DavidZ770,
First, if you haven't yet, try restarting your Mac to see if it helps. Sometimes, restarting can help many unknown issues.
If that didn't help, see if this happens with only Facebook and Twitter to help us further isolate the issue. For example, try open the Photos app and see if it allows you to open the selected photos you wanted. If you can, then we know that the issue isn't coming from your Photos app,
Also, test this out on a different web browser such as Google Chrome, Firefox or Safari. Be sure to test it out on a web browser you haven't tested this before.
Please let us know how it goes after following all the steps we provided above.
Cheers!