Features implemented only in Firefox

The following features are only implemented in Firefox.

• Alternative style sheets

  Limited availability

  The rel="alternate stylesheet" attribute for the <link> HTML element offers an alternative style option to users.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 3 Released on 2008-06-17
  • Firefox for Android 4 Released on 2011-03-29
  • Safari Not supported
  • Safari on iOS Not supported

• Anchor positioning

  Limited availability

  Anchor positioning places an element based on the position of another element. For example, you can place a tooltip next to the content it references.

  Learn more

  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 151 Released on 2026-05-19
  • Firefox for Android 151 Released on 2026-05-19
  • Safari Not supported Position: support
  • Safari on iOS Not supported Position: support

• ariaNotify()

  Limited availability

  The ariaNotify() method of Element and Document requests assistive technology software, if activated, to announce a message to the user. This can help make dynamic content changes more accessible to users.

  Learn more

  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 150 Released on 2026-04-21
  • Firefox for Android 150 Released on 2026-04-21
  • Safari Not supported Position: support
  • Safari on iOS Not supported Position: support

• Case-sensitive attribute selector

  Limited availability

  The s identifier in a CSS attribute selector matches attribute values case-sensitively in document languages like HTML where attribute values are case-insensitive.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 66 Released on 2019-03-19
  • Firefox for Android 66 Released on 2019-03-19
  • Safari Not supported
  • Safari on iOS Not supported

• color-mix() with three or more colors

  Limited availability

  The color-mix() CSS function accepts three or more colors.

  Learn more

  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 150 Released on 2026-04-21
  • Firefox for Android 150 Released on 2026-04-21
  • Safari Not supported
  • Safari on iOS Not supported

• Reversed counter-reset

  Limited availability

  The reversed() CSS function for counter-reset creates a counter that counts down.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 96 Released on 2022-01-11
  • Firefox for Android 96 Released on 2022-01-11
  • Safari Not supported
  • Safari on iOS Not supported

• Custom ellipses

  Limited availability

  The text-overflow CSS property with a string value sets the string representing clipped text.

  Learn more

  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 9 Released on 2011-12-20
  • Firefox for Android 9 Released on 2011-12-21
  • Safari Not supported
  • Safari on iOS Not supported

• display: ruby

  Limited availability

  The display: ruby CSS declaration renders an element with the box layout of a <ruby> HTML element. Child elements may use equivalents to <ruby> internal elements such as display: ruby-base for <rb>.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 88 Released on 2021-04-19
  • Firefox for Android 88 Released on 2021-04-19
  • Safari Not supported
  • Safari on iOS Not supported

• Early data

  Limited availability

  TLS 1.3 sessions may be resumed more quickly by sending so-called early data to servers before the TLS handshake has finished. Also known as zero round-trip time resumption or 0-RTT.

  Learn more

  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 58 Released on 2018-01-23
  • Firefox for Android 58 Released on 2018-01-22
  • Safari Not supported
  • Safari on iOS Not supported

• font-synthesis-position

  Limited availability

  The font-synthesis-position CSS property sets whether or not the browser should synthesize subscript and superscript typefaces when they're missing from the font.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 118 Released on 2023-09-26
  • Firefox for Android 118 Released on 2023-09-26
  • Safari Not supported
  • Safari on iOS Not supported

• font-variant-position

  Limited availability

  The font-variant-position CSS property sets whether to use alternate glyphs for subscript and superscript text.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 34 Released on 2014-12-01
  • Firefox for Android 34 Released on 2014-12-01
  • Safari Not supported
  • Safari on iOS Not supported

• Gamepad VR hands and poses

  Limited availability

  The hand and pose properties of a Gamepad object represent the position in space and the hand that WebVR controllers are held in.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 55 Released on 2017-08-08
  • Firefox for Android 55 Released on 2017-08-08
  • Safari Not supported Position: support
  • Safari on iOS Not supported Position: support

• Global privacy control

  Limited availability

  The Sec-GPC request header indicates that the user does not consent to a website or service selling or sharing their personal information with third parties.

  Learn more

  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 120 Released on 2023-11-21
  • Firefox for Android 122 Released on 2024-01-23
  • Safari Not supported
  • Safari on iOS Not supported

• :has-slotted

  Limited availability

  The :has-slotted CSS pseudo-class matches <slot> elements where the fallback content is not shown. The pseudo-class matches any slotted content, including white space, text nodes, or elements.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 136 Released on 2025-03-04
  • Firefox for Android 136 Released on 2025-03-04
  • Safari Not supported Position: support
  • Safari on iOS Not supported Position: support

• ime-mode

  The ime-mode CSS property sets the state of the input method editor for text fields.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 3 Released on 2008-06-17
  • Firefox for Android 4 Released on 2011-03-29
  • Safari Not supported
  • Safari on iOS Not supported

• light-dark() image values

  Limited availability

  The light-dark() CSS function accepts, in addition to colors, two <image> values, such as a gradient or URL, and uses one depending on the current color scheme.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 150 Released on 2026-04-21
  • Firefox for Android 150 Released on 2026-04-21
  • Safari Not supported
  • Safari on iOS Not supported

• overflow-clip-margin

  Limited availability

  The overflow-clip-margin CSS property sets how far overflow content may appear outside the bounds of an element before it's clipped by effects such as overflow: clip.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 148 Released on 2026-02-24
  • Firefox for Android 148 Released on 2026-02-24
  • Safari Not supported Position
  • Safari on iOS Not supported Position

• ReadableStream.from()

  Limited availability

  The ReadableStream.from() static method converts an iterable or async iterable object, such as an array or async generator function, into a readable stream.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 117 Released on 2023-08-29
  • Firefox for Android 117 Released on 2023-08-29
  • Safari Not supported
  • Safari on iOS Not supported

• Sanitizer API

  Limited availability

  The Document.parseHTML() static method and the setHTML() method of Element and ShadowRoot objects parse and insert HTML into the DOM in a way that can prevent cross-site scripting attacks. The Sanitizer API can customize the sanitization process.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 148 Released on 2026-02-24
  • Firefox for Android 148 Released on 2026-02-24
  • Safari Not supported
  • Safari on iOS Not supported

• image-rendering: smooth

  Limited availability

  The image-rendering: smooth CSS declaration scales images while retaining a gradual color blending that is useful for photos.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 93 Released on 2021-10-05
  • Firefox for Android 93 Released on 2021-10-05
  • Safari Not supported
  • Safari on iOS Not supported

• video-dynamic-range media query

  Limited availability

  The video-dynamic-range CSS media query sets styles based on whether a device can display video with at least standard range colors or at least high range colors. Non-visual devices will match neither.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 100 Released on 2022-05-03
  • Firefox for Android 100 Released on 2022-05-03
  • Safari Not supported
  • Safari on iOS Not supported

• WebDriver

  Limited availability

  The WebDriver protocol allows out-of-process programs to inspect and control browsers to, for example, run tests of web applications. Also known as WebDriver classic.

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  • Chrome Not supported
  • Chrome Android Not supported
  • Edge Not supported
  • Firefox 66 Released on 2019-03-19
  • Firefox for Android Not supported
  • Safari Not supported
  • Safari on iOS Not supported