You must have the layout set to "Disabled", where the video player is not supposed to be squared (the black pixels around the player is actually a bug, the whole thing is supposed to remain rounded). Try setting the layout to anything else (2021 is the closest to the current layout), and the video should be squared.

Edit: To change settings, pin the extension to the toolbar, then click on the icon to make the config window pop up. Here's how you do that: https://imgur.com/a/IIxddDa

Yes, that does seem to happen on some videos. I'll look into it.

Edit: Yes, you can report bugs to the CustomTube Github: https://github.com/lightbeam24/CustomTube/issues

Thanks!

I downloaded Firefox 102 ESR to test, and I was able to edit the settings just fine. Are you sure you found the popup with all the settings? A few users reported not being able to find it at first. The CustomTube icon should be either on your browser toolbar, or in the Extensions list (by clicking on the extensions button beside Firefox's menu button). Click the icon to open the popup.

If you actually did find the popup and were still unable to change settings, please consider making an issue on the CustomTube Github: https://github.com/lightbeam24/customtube/issues

As for the subscription page thumbnails, YouTube has been A/B testing a new icon system, where the icons take much longer to load. Try refreshing the page while on the subscriptions page, and wait 5-10 seconds. The 3 dots should have appeared by then.

Glad you like it! I'll look into that sometime.