Honestly great and advertises exactly what it does. However, I believe I found a bug that could have occurred through one of YouTube's updates. It was working great up until a couple days ago. Thumbnails for suggested videos to the right of the video-player have reverted back to having their rounded corners. Although things like the homepage thumbnails, subscription thumbnails, and channel thumbnails all still appear with sharp edges. I have seen this bug happen on both PC and Mac for the Firefox browser.

I have not seen a way of contacting the maker of this extension other than a link to his GitHub page. I don't want to have to make an account solely just for that.

this does exactly what i wanted, unrounded videos and thumbnails but not the whole interface, very nice.

It works! Next up: square buttons and avatars like another reviewer also said. My request: Please also develop this for Chromium browsers too if you can. Thanks in advance!