This release adds the sibling-count() and sibling-index() CSS functions, the text-box-trim, text-box-edge, and text-box properties for trimming space above and below text, and the Iterator methods includes(), join(), chunks(), and windows(). WebRTC gains getSelectedCandidatePair(). Behind flags: unprefixed line-clamp, percentages for text-decoration-inset, the progress() function, and CSS Typed OM.
developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/154