Mozilla plans to enable JPEG XL decoding by default in Firefox 157, which is due at the end of September. Phoronix reports: Firefox Nightly has JPEG-XL support enabled by default right now to help in vetting this support while Mozilla believes the support is in good enough shape for a stable debut with Firefox 157. This follows Chrome shipping JPEG-XL and Google Research developing jxl-rs as a Rust-based JPEG-XL image decoder that is both performant and secure.
In today's Mozilla Hacks blog post they elaborate on JPEG-XL vs. AVIF image formats: "JPEG XL: Excels at lossless imagery, progressive rendering, and further compressing JPEGs without quality loss. AVIF: Excels at web-quality photographic images, and images that have a mix of sharp edges and flat surfaces. ... Although AVIF tends to produce smaller files at web-quality than JPEG XL, AVIF only has basic progressive rendering support. So, for very large images, it may be worth taking the filesize hit with JPEG XL."