Firefox 159 ships scroll-driven animations by default
Firefox was the last major browser holding this behind a flag. With 159 out, animation-timeline works without JavaScript everywhere that matters.
Firefox 159 shipped today, 27 October, and turns on scroll-driven animations by default. The feature lets you animate a property along a scroll-based timeline instead of the usual time-based one, using the animation-timeline property, with no JavaScript required.
Chrome and Edge have supported this unflagged since version 115, back in July 2023. Safari followed in version 26, last September. Firefox was sitting behind a flag in stable as recently as version 152, so 159 closes out the set of major engines.
The same release removes the legacy masonry value from grid-template-columns and grid-template-rows, replacing it with the newer grid lanes layout. The HTML Sanitizer API also changed: methods like Element.setHTML() now strip unwanted elements and attributes during parsing rather than after, so neighbouring text lands in one text node instead of being split apart.
Why it matters: scroll-linked effects like progress bars, parallax and reveal-on-scroll animations have needed a scroll event listener and manual JavaScript for years. With Firefox caught up, animation-timeline works across every major engine without a fallback, so it is safe to reach for in production CSS rather than behind a feature check.
.progress {
animation: grow linear;
animation-timeline: scroll(root block);
}