Both JPEG XL and AVIF support is already there in Chrome and Firefox, and can be enabled with about:config or command-line flags. AVIF will become supported by

Both JPEG XL and AVIF support is already there in Chrome and Firefox, and can be enabled with about:config or command-line flags. AVIF will become supported by default in the very next version of Firefox and is already supported by Chrome. Edge mysteriously does not yet support AVIF despite building on the same Chromium base that does support it, which means the AVIF code is deliberately compiled out by MS for some reason. Safari is a different kettle of fish. It supports neither format yet, but there seem to be vague indications on the issue tracker that one day they may land AVIF support. For that matter even Webp support is confined to only Safari on Big Sur and later, according to caniuse. It truly is shaping up to take over IE soon, as the browser for which one has to go to great lengths to code fallbacks.