October 27, 2026. Firefox 158, released October 13, adds support for JPEG XL. It is an image-format change worth noticing, but not a reason to convert an entire photo library without testing the tools around it.
Mozilla lists the addition in its official release notes. The JPEG committee’s format overview describes support for lossy and lossless coding, wide colour gamut and high dynamic range. It also describes reversible transcoding of existing JPEG files into JPEG XL.
A smaller file is only part of the decision
The format’s designers emphasize fidelity, compression and processing speed. Those are design goals and capabilities, not a promise that every image will shrink by the same amount. This article does not report an independent compression benchmark.
For a publisher, the useful experiment is a representative sample: photographs, graphics with text and anything with transparency that the actual site uses. Compare the resulting appearance and file size, then check the image-processing and delivery chain.
Keep the fallback until you have tested the route
One browser’s support does not establish support in every recipient’s browser, editing application, content-management system or image service. Test the environments your readers actually use and retain a compatible alternative where needed.
Keep original source files too. A delivery-format experiment should be reversible, and a successful local preview is not the same thing as a successful upload, thumbnail generation and public download.
Featured photo: Nicolas Gonzalez / Unsplash, used under the Unsplash License. Illustrative stock photograph.
