Refractive Glass: Noise Bends the Backdrop
Chrome is the only engine that bends a real backdrop. Safari and Firefox run an SVG filter on an element and never on a backdrop, so there it is a copy of the scene's own gradient that bends, and over arbitrary content they get the frost and nothing else. Frosted glass blurs what is behind it; real glass moves it. feTurbulence paints a cloud, feDisplacementMap reads red as how far each backdrop pixel travels along x and green as y, and it runs before the blur averages anything. The lens and the frost are siblings, never nested: an element with a backdrop-filter starts its own backdrop root, so a lens inside the frosted box would find nothing left to bend. The filter travels as a data URI because a fragment reference cannot be resolved from a sandboxed frame.