Firefox 158 Turns On JPEG XL and Typed CSS Math

Firefox 158 shipped on October 13 and enables JPEG XL by default. That gives image pipelines a second major engine for the format, alongside Chrome 155, which added its Rust-based JXL decoder earlier this month. Do not drop your AVIF and WebP fallbacks yet; keep them until every engine you support decodes JXL.

The CSS change is typed arithmetic in calc(). Firefox now lets math functions operate on typed values, so you can multiply and divide units inside a calculation instead of adding a JavaScript measurement pass. If you compute ratios or fluid values in script today, test whether calc() can replace that work.

Two smaller platform additions matter for app code. Notifications gain a navigate option in the constructor and ServiceWorkerRegistration.showNotification(), which sets where a click lands. WebAuthn conditional UI now appears for inputs with only autocomplete="webauthn", rather than requiring another autofill token. PerformanceResourceTiming.deliveryType also gains a cache value, so your RUM data can separate cache hits from network responses.

The release carries 77 security fixes, 30 of them high severity, including sandbox escapes and JIT miscompilation. Update desktop and Android builds, then re-run your image and CSS snapshot tests; the JXL and calc() changes are the ones most likely to move pixels.