I am the owner of a 21:9 monitor and was very happy to see this extension. It's really very useful, I'm afraid to imagine how useful it is for users of extra wide monitors. But the problem is that the default value for the width of the site is quite small.

“But you can increase that width, right?”

Yes, but at least it doesn't work for me, I've turned the module on and off, changed the default value via extension settings and nothing. As it was 960, so it remains. I'll leave the extension, it still helps a lot on some sites, but I'm really looking forward to a fix so I and other users can enjoy it fully