What sites are broken by RFP/LibreWolf?

This come from disabled HTML5 canvas image data and can be easily turned on per site. If you encounter such things, left site of the URL there is a toolbar (inlc. Shield, lock, settings icon) there will pop up a new icon, which looks like a picture, where you can click on an activate HTML5 canvas. Here is how this icon looks in Mullvad (will nearly look the same all Firefox based browser) Now just click on the new “image-like”-icon and then press the “allow” button. After that reload the image or the whole page with the “reload”-icon. Due how powerful canvas image data are it can lead to more sophisticated tracking and even exploits. Therefor most secure browser like Mullvad-Browser, Tor-Browser or LibreWolf, disable canvas image data per default.