The release adds sizes="auto" for lazy-loaded images, color-mix() with multiple colors, light-dark() with image values, media pseudo-classes like :buffering, :paused, and :playing for <audio> and <video> elements, animation range properties for scroll-driven animations, the revert-rule keyword, ariaNotify() for screen reader announcements, and an overscroll-behavior fix for elements with overflow: hidden.
developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/150