Add-ons • Re: is there an addon to rip content protected images?

https://www.w3schools.com/graphics/canvas_images.asp

Pale Moon saves canvas contents to a file without any problems. "Save image as..." is available in the context menu. It's possible that in the case described by the OP, the image (img or canvas) is obscured by some transparent element, causing the browser to see the overlying element rather than the actual image source.