New features in Firefox 155 (released on 2026-09-01)

• alpha()

  Limited availability

  The alpha() CSS function computes a relative color value by adjusting the opacity of an origin color.

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  • Chrome 151 Released on 2026-07-28
  • Chrome Android 151 Released on 2026-07-28
  • Edge 151 Released on 2026-07-31
  • Firefox 155 Released on 2026-09-01
  • Firefox for Android 155 Released on 2026-09-01
  • Safari Not supported
  • Safari on iOS Not supported

  Baseline availability blocked since September 2026 by Safari (0 months)

• attr()

  Limited availability

  The attr() CSS function, in the context of any property, returns the value of an attribute of an HTML element, with the option to return it as a specific type or unit. You can set a default value for missing or invalid attributes.

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  • Chrome 133 Released on 2025-02-04
  • Chrome Android 133 Released on 2025-02-04
  • Edge 133 Released on 2025-02-06
  • Firefox 155 Released on 2026-09-01
  • Firefox for Android 155 Released on 2026-09-01
  • Safari Not supported
  • Safari on iOS Not supported

  Baseline availability blocked since September 2026 by Safari (0 months)

• progress()

  Newly Available (since 2026-09-01)

  The progress() CSS function returns a ratio for the relative position of one value between two other values, clamped between 0 and 1. You can use it to interpolate a value for other calculations.

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  • Chrome 138 Released on 2025-06-24
  • Chrome Android 138 Released on 2025-06-24
  • Edge 138 Released on 2025-06-26
  • Firefox 155 Released on 2026-09-01
  • Firefox for Android 155 Released on 2026-09-01
  • Safari 26 Released on 2025-09-15
  • Safari on iOS 26 Released on 2025-09-15