New features in Firefox 154 (released on 2026-08-18)

• sibling-count() and sibling-index()

  Newly Available (since 2026-08-18)

  The sibling-count() and sibling-index() CSS functions return integers that are useful to style elements based on their positions among siblings or on the number of siblings, for example as part of a calc() expression.

  Learn more

  • Chrome 138 Released on 2025-06-24
  • Chrome Android 138 Released on 2025-06-24
  • Edge 138 Released on 2025-06-26
  • Firefox 154 Released on 2026-08-18
  • Firefox for Android 154 Released on 2026-08-18
  • Safari 26.2 Released on 2025-12-12
  • Safari on iOS 26.2 Released on 2025-12-12