So Youtube rolled out new layout again and while doing so they removed the sorting options in filters. I remade an extension for FF so that it would work in Opera.
Enlarges thumbnails and linked images (or even linked thumbnails) into a popup with just a mouse hover. As well as the Viewer, it's also fairly customizable with some extra features, such as full-zoom which allows you to view the image with original size in the same tab, rotation or it can load image albums as well.
Imagus has Hover Zoom: Works perfectly.