Firefox 157 to Enable JPEG XL Decoding by Default Across All Platforms

Default JPEG XL Support in Firefox 157

Firefox 157 will activate JPEG XL (JXL) image decoding by default across all supported platforms. This feature has been under development behind the `image.jxl.enabled` preference, which was previously only enabled by default in Nightly builds and available via a Firefox Labs checkbox since version 152.

Technical Implementation and Performance

The JXL decoder used in Firefox is `jxl-rs`, written in Rust. Performance concerns raised during the intent to prototype phase have been addressed with the release of `jxl-rs 0.6.0`, which includes multithreaded decoding support. Benchmarks indicate that Firefox's JXL decoding performance is slightly ahead of Safari's C++ libjxl implementation and is competitive with Firefox's other image format decoders, particularly for large images.

Feature Parity and Enhancements

The Firefox JXL implementation offers feature parity with other image formats supported by the browser and with Blink's JXL implementation. This includes support for animation and progressive display. While HDR images will display as SDR, the tone mapping for JXL is noted to be significantly better than for other image formats in Firefox. Safari's JXL implementation lacks progressive rendering and animation.

Testing and Standards Position

Extensive testing has been conducted, covering decode correctness across various parameters like bit depths, alpha channels, grayscale, CMYK, color management, and orientation, using both web platform tests (WPT) and Gecko-specific tests. These include tests for chunked and incremental decoding, animation frame counts, downscaling during decode, and corrupt files. Mozilla's standards position on JPEG XL is neutral, and the W3C TAG review was satisfied with concerns.