Firefox doesn't decode the image into a full-resolution buffer and then downscale either, instead it does a streaming decode and applies downscaling on the fly.

Firefox doesn't decode the image into a full-resolution buffer and then downscale either, instead it does a streaming decode and applies downscaling on the fly. They call it downscale-during-decode[0]. I guess it doesn't do partial decoding of the 8x8 blocks though. [0] https://bugzilla.mozilla.org/show_bug.cgi?id=1045926 https://bugzilla.mozilla.org/show_bug.cgi?id=1045926