Experimental

For a given set of browsers what APIs are still considred experimental, and how long have they been experimental?

Example Comparisons
Browsers
Features

Summary

Experimental APIs

Below is a list of features that are marked as "Experimental" in Firefox and Safari on iOS

Raw Data

Quick Links:

CSS Data

API First Browser Date Last Browser Date Days in experimentation Notes
css.at-rules.custom-media 📋Firefox2/24/2026 111
css.at-rules.media.prefers-reduced-transparency 📋Firefox5/9/2023 1133
css.properties.-webkit-column-axis Safari on iOS9/10/2012 5026
css.properties.-webkit-column-progression Safari on iOS9/18/2013 4653
css.properties.-webkit-cursor-visibility Safari on iOS9/18/2013 4653
css.properties.-webkit-hyphenate-limit-after Safari on iOS10/12/2011 5360
css.properties.-webkit-hyphenate-limit-before Safari on iOS10/12/2011 5360
css.properties.-webkit-hyphenate-limit-lines Safari on iOS9/10/2012 5026
css.properties.-webkit-line-align Safari on iOS9/10/2012 5026
css.properties.-webkit-line-box-contain Safari on iOS10/12/2011 5360
css.properties.-webkit-line-grid Safari on iOS9/10/2012 5026
css.properties.-webkit-line-snap Safari on iOS9/10/2012 5026
css.properties.-webkit-mask-source-type Safari on iOS9/18/2013 4653
css.properties.-webkit-nbsp-mode Safari on iOS4/3/2010 5917
css.properties.-webkit-text-zoom Safari on iOS9/13/2016 3562
css.properties.background.x-end 📋Safari on iOS9/15/2025 273
css.properties.background.x-start 📋Safari on iOS9/15/2025 273
css.properties.background.y-end 📋Safari on iOS9/15/2025 273
css.properties.background.y-start 📋Safari on iOS9/15/2025 273
css.properties.background-image.element 📋Firefox3/22/2011 5564
css.properties.background-position.x-end 📋Safari on iOS9/15/2025 273
css.properties.background-position.x-start 📋Safari on iOS9/15/2025 273
css.properties.background-position.y-end 📋Safari on iOS9/15/2025 273
css.properties.background-position.y-start 📋Safari on iOS9/15/2025 273
css.properties.background-position-x.x-end 📋Safari on iOS9/15/2025 273
css.properties.background-position-x.x-start 📋Safari on iOS9/15/2025 273
css.properties.background-position-y.y-end 📋Safari on iOS9/15/2025 273
css.properties.background-position-y.y-start 📋Safari on iOS9/15/2025 273
css.properties.block-size.fit-content_function Firefox8/10/2021 1770
css.properties.break-after.always Firefox1/29/2019 2694
css.properties.break-before.always Firefox1/29/2019 2694
css.properties.content.none_applies_to_elements Firefox8/10/2021 1770
css.properties.counter-reset.reset_does_not_affect_siblings Firefox10/20/2020 2064
css.properties.counter-reset.reversed 📋Firefox1/11/2022 1616
css.properties.font-synthesis-position 📋Firefox9/26/2023 993
css.properties.font-synthesis-position.auto 📋Firefox9/26/2023 993
css.properties.font-synthesis-position.none 📋Firefox9/26/2023 993
css.properties.font-synthesis-style.oblique-only 📋Firefox4/1/2025 440
css.properties.grid-template-columns.masonry 📋Firefox6/2/2020 2204
css.properties.grid-template-rows.masonry 📋Firefox6/2/2020 2204
css.properties.height.fit-content_function 📋Firefox8/10/2021 1770
css.properties.image-rendering.smooth 📋Firefox10/5/2021 1714
css.properties.inline-size.fit-content_function Firefox8/10/2021 1770
css.properties.margin-trim 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.block 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.block-end 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.block-start 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.inline 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.inline-end 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.inline-start 📋Safari on iOS3/27/2023 1176
css.properties.margin-trim.none 📋Safari on iOS3/27/2023 1176
css.properties.mask.x-end 📋Safari on iOS9/15/2025 273
css.properties.mask.x-start 📋Safari on iOS9/15/2025 273
css.properties.mask.y-end 📋Safari on iOS9/15/2025 273
css.properties.mask.y-start 📋Safari on iOS9/15/2025 273
css.properties.mask-position.x-end 📋Safari on iOS9/15/2025 273
css.properties.mask-position.x-start 📋Safari on iOS9/15/2025 273
css.properties.mask-position.y-end 📋Safari on iOS9/15/2025 273
css.properties.mask-position.y-start 📋Safari on iOS9/15/2025 273
css.properties.max-block-size.fit-content_function Firefox8/10/2021 1770
css.properties.max-height.fit-content_function 📋Firefox8/10/2021 1770
css.properties.max-inline-size.fit-content_function Firefox8/10/2021 1770
css.properties.max-width.fit-content_function 📋Firefox8/10/2021 1770
css.properties.min-block-size.fit-content_function Firefox8/10/2021 1770
css.properties.min-height.fit-content_function 📋Firefox8/10/2021 1770
css.properties.min-inline-size.fit-content_function Firefox8/10/2021 1770
css.properties.min-width.fit-content_function 📋Firefox8/10/2021 1770
css.properties.mix-blend-mode.plus-darker 📋Safari on iOS9/16/2015 3925
css.properties.object-position.x-end 📋Safari on iOS9/15/2025 273
css.properties.object-position.x-start 📋Safari on iOS9/15/2025 273
css.properties.object-position.y-end 📋Safari on iOS9/15/2025 273
css.properties.object-position.y-start 📋Safari on iOS9/15/2025 273
css.properties.offset.margin-box 📋Safari on iOS9/12/2022 1372
css.properties.offset.x-end 📋Safari on iOS9/15/2025 273
css.properties.offset.x-start 📋Safari on iOS9/15/2025 273
css.properties.offset.y-end 📋Safari on iOS9/15/2025 273
css.properties.offset.y-start 📋Safari on iOS9/15/2025 273
css.properties.offset-anchor.x-end 📋Safari on iOS9/15/2025 273
css.properties.offset-anchor.x-start 📋Safari on iOS9/15/2025 273
css.properties.offset-anchor.y-end 📋Safari on iOS9/15/2025 273
css.properties.offset-anchor.y-start 📋Safari on iOS9/15/2025 273
css.properties.offset-path.margin-box 📋Safari on iOS9/16/2024 637
css.properties.offset-position.x-end 📋Safari on iOS9/15/2025 273
css.properties.offset-position.x-start 📋Safari on iOS9/15/2025 273
css.properties.offset-position.y-end 📋Safari on iOS9/15/2025 273
css.properties.offset-position.y-start 📋Safari on iOS9/15/2025 273
css.properties.perspective-origin.x-end 📋Safari on iOS9/15/2025 273
css.properties.perspective-origin.x-start 📋Safari on iOS9/15/2025 273
css.properties.perspective-origin.y-end 📋Safari on iOS9/15/2025 273
css.properties.perspective-origin.y-start 📋Safari on iOS9/15/2025 273
css.properties.ruby-position.alternate Firefox4/19/2021 1883
css.properties.speak-as 📋Safari on iOS3/29/2018 3000
css.properties.speak-as.digits 📋Safari on iOS3/29/2018 3000
css.properties.speak-as.literal-punctuation 📋Safari on iOS3/29/2018 3000
css.properties.speak-as.no-punctuation 📋Safari on iOS3/29/2018 3000
css.properties.speak-as.normal 📋Safari on iOS3/29/2018 3000
css.properties.speak-as.spell-out 📋Safari on iOS3/29/2018 3000
css.properties.stroke-color 📋Safari on iOS3/29/2018 3000
css.properties.stroke-color.currentColor 📋Safari on iOS3/29/2018 3000
css.properties.stroke-color.transparent 📋Safari on iOS3/29/2018 3000
css.properties.text-align-last.match-parent 📋Safari on iOS9/12/2022 1372
css.properties.text-autospace.insert 📋Firefox11/11/2025 216
css.properties.text-box.cap 📋Safari on iOS12/11/2024 551
css.properties.text-box.ex 📋Safari on iOS12/11/2024 551
css.properties.text-box.ideographic 📋Safari on iOS12/11/2024 551
css.properties.text-box.ideographic-ink 📋Safari on iOS12/11/2024 551
css.properties.text-box-edge.cap 📋Safari on iOS12/11/2024 551
css.properties.text-box-edge.ex 📋Safari on iOS12/11/2024 551
css.properties.text-box-edge.ideographic 📋Safari on iOS12/11/2024 551
css.properties.text-box-edge.ideographic-ink 📋Safari on iOS12/11/2024 551
css.properties.text-decoration-inset 📋Firefox12/9/2025 188
css.properties.text-decoration-inset.auto 📋Firefox12/9/2025 188
css.properties.text-decoration-skip 📋Safari on iOS3/25/2019 2639
Chrome: Only supported the deprecated ink value.Chrome Android: Only supported the deprecated ink value.Opera: Only supported the deprecated ink value.Opera Android: Only supported the deprecated ink value.Samsung Internet: Only supported the deprecated ink value.WebView Android: Only supported the deprecated ink value.
css.properties.text-decoration-skip.auto 📋Safari on iOS9/18/2013 4653
css.properties.text-decoration-skip.none 📋Safari on iOS9/18/2013 4653
css.properties.text-emphasis-position.auto Firefox10/29/2024 594
css.properties.text-size-adjust 📋Safari on iOS6/29/2007 6926
css.properties.white-space.preserve-spaces 📋Firefox3/19/2024 818
css.properties.white-space-collapse.preserve-spaces 📋Firefox3/19/2024 818
css.properties.width.fit-content_function 📋Firefox8/10/2021 1770
css.selectors.-moz-first-node Firefox8/8/2017 3233
css.selectors.-moz-last-node Firefox8/8/2017 3233
css.selectors.-moz-list-bullet Firefox11/9/2004 7888
css.selectors.-moz-list-number Firefox11/9/2004 7888
css.selectors.-moz-progress-bar Firefox8/16/2011 5417
css.selectors.marker.counter_support 📋Firefox1/13/2026 153
css.selectors.marker.quotes_support 📋Firefox1/13/2026 153
css.types.image.element 📋Firefox11/14/2017 3135
Firefox: -moz-element() is limited to background-image, background, border-image and border-image-source.Firefox: -moz-element() is limited to background-image and background.Firefox for Android: -moz-element() is limited to background-image, background, border-image and border-image-source.Firefox for Android: -moz-element() is limited to background-image and background.
css.types.random 📋Safari on iOS12/12/2025 185
css.types.random.dashed-ident 📋Safari on iOS12/12/2025 185
css.types.random.element-shared 📋Safari on iOS12/12/2025 185
css.types.random.step 📋Safari on iOS12/12/2025 185
css.types.ratio.number_value Firefox6/30/2020 2176

HTML Data

API First Browser Date Last Browser Date Days in experimentation Notes
html.elements.a.attributionsourceid 📋Safari on iOS4/26/2021 1876
html.elements.iframe.allow.document-domain 📋Firefox3/10/2020 2288
html.elements.iframe.allow.gamepad 📋Firefox8/10/2021 1770
Firefox: The default allowlist is * instead of self (as required by the specification).Firefox for Android: The default allowlist is * instead of self (as required by the specification).
html.elements.iframe.allow.speaker-selection 📋Firefox8/1/2023 1049
Firefox for Android: Not available due to a limitation in Android (see bug 1473346).
html.elements.input.alpha 📋Safari on iOS3/31/2025 441
html.elements.input.colorspace 📋Safari on iOS3/31/2025 441
html.elements.input.switch Safari on iOS3/5/2024 832
html.elements.script.type.speculationrules 📋Safari on iOS12/12/2025 185
Chrome: Initial support included same-origin prerendering only.Chrome Android: Initial support included same-origin prerendering only.Edge: Initial support included same-origin prerendering only.Quest Browser: Initial support included same-origin prerendering only.Opera: Initial support included same-origin prerendering only.Opera Android: Initial support included same-origin prerendering only.Samsung Internet: Initial support included same-origin prerendering only.WebView Android: Initial support included same-origin prerendering only.
html.elements.script.type.speculationrules.eagerness 📋Safari on iOS12/12/2025 185
Safari: Only conservative is supported for document rules (though moderate automatically falls back to conservative). Only eager and immediate is supported for list rules.Safari on iOS: Only conservative is supported for document rules (though moderate automatically falls back to conservative). Only eager and immediate is supported for list rules.
html.elements.script.type.speculationrules.prefetch 📋Safari on iOS12/12/2025 185
html.elements.script.type.speculationrules.referrer_policy 📋Safari on iOS12/12/2025 185
html.elements.script.type.speculationrules.relative_to 📋Safari on iOS12/12/2025 185
html.elements.script.type.speculationrules.source_optional 📋Safari on iOS12/12/2025 185
html.elements.script.type.speculationrules.tag 📋Safari on iOS12/12/2025 185
html.elements.script.type.speculationrules.urls 📋Safari on iOS12/12/2025 185
html.elements.script.type.speculationrules.where 📋Safari on iOS12/12/2025 185
html.elements.template.shadowrootreferencetarget Safari on iOS9/15/2025 Firefox3/24/2026190