For a given set of browsers what APIs are still considred experimental, and how long have they been experimental?
Below is a list of features that are marked as "Experimental" in Firefox and Safari
| API | First Browser | Date | Last Browser | Date | Days in experimentation | Notes |
|---|---|---|---|---|---|---|
| css.at-rules.custom-media 📋 | Firefox | 2/24/2026 | 120 | |||
| css.at-rules.font-face.font-width 📋 | Safari | 3/31/2025 | 450 | |||
| css.at-rules.media.prefers-reduced-transparency 📋 | Firefox | 5/9/2023 | 1142 | |||
| css.properties.-webkit-column-axis | Safari | 7/25/2012 | 5082 | |||
| css.properties.-webkit-column-progression | Safari | 10/22/2013 | 4628 | |||
| css.properties.-webkit-cursor-visibility | Safari | 10/22/2013 | 4628 | |||
| css.properties.-webkit-hyphenate-limit-after | Safari | 7/20/2011 | 5453 | |||
| css.properties.-webkit-hyphenate-limit-before | Safari | 7/20/2011 | 5453 | |||
| css.properties.-webkit-hyphenate-limit-lines | Safari | 7/25/2012 | 5082 | |||
| css.properties.-webkit-line-align | Safari | 7/25/2012 | 5082 | |||
| css.properties.-webkit-line-box-contain | Safari | 7/20/2011 | 5453 | |||
| css.properties.-webkit-line-grid | Safari | 7/25/2012 | 5082 | |||
| css.properties.-webkit-line-snap | Safari | 7/25/2012 | 5082 | |||
| css.properties.-webkit-mask-source-type | Safari | 10/22/2013 | 4628 | |||
| css.properties.-webkit-nbsp-mode | Safari | 6/8/2009 | 6225 | |||
| css.properties.-webkit-text-zoom | Safari | 9/20/2016 | 3564 | |||
| css.properties.background.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-image.element 📋 | Firefox | 3/22/2011 | 5573 | |||
| css.properties.background-position.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position-x.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position-x.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position-y.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.background-position-y.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.block-size.fit-content_function | Firefox | 8/10/2021 | 1779 | |||
| css.properties.break-after.always | Firefox | 1/29/2019 | 2703 | |||
| css.properties.break-before.always | Firefox | 1/29/2019 | 2703 | |||
| css.properties.content.none_applies_to_elements | Firefox | 8/10/2021 | 1779 | |||
| css.properties.counter-reset.reset_does_not_affect_siblings | Firefox | 10/20/2020 | 2073 | |||
| css.properties.counter-reset.reversed 📋 | Firefox | 1/11/2022 | 1625 | |||
| css.properties.font-synthesis-position 📋 | Firefox | 9/26/2023 | 1002 | |||
| css.properties.font-synthesis-position.auto 📋 | Firefox | 9/26/2023 | 1002 | |||
| css.properties.font-synthesis-position.none 📋 | Firefox | 9/26/2023 | 1002 | |||
| css.properties.font-synthesis-style.oblique-only 📋 | Firefox | 4/1/2025 | 449 | |||
| css.properties.font-width 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.condensed 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.expanded 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.extra-condensed 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.extra-expanded 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.normal 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.percentage 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.semi-condensed 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.semi-expanded 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.ultra-condensed 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.font-width.ultra-expanded 📋 | Safari | 3/31/2025 | 450 | |||
| css.properties.grid-template-columns.masonry 📋 | Firefox | 6/2/2020 | 2213 | |||
| css.properties.grid-template-rows.masonry 📋 | Firefox | 6/2/2020 | 2213 | |||
| css.properties.height.fit-content_function 📋 | Firefox | 8/10/2021 | 1779 | |||
| css.properties.image-rendering.smooth 📋 | Firefox | 10/5/2021 | 1723 | |||
| css.properties.inline-size.fit-content_function | Firefox | 8/10/2021 | 1779 | |||
| css.properties.margin-trim 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.block 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.block-end 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.block-start 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.inline 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.inline-end 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.inline-start 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.margin-trim.none 📋 | Safari | 3/27/2023 | 1185 | |||
| css.properties.mask.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask-position.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask-position.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask-position.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.mask-position.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.max-block-size.fit-content_function | Firefox | 8/10/2021 | 1779 | |||
| css.properties.max-height.fit-content_function 📋 | Firefox | 8/10/2021 | 1779 | |||
| css.properties.max-inline-size.fit-content_function | Firefox | 8/10/2021 | 1779 | |||
| css.properties.max-width.fit-content_function 📋 | Firefox | 8/10/2021 | 1779 | |||
| css.properties.min-block-size.fit-content_function | Firefox | 8/10/2021 | 1779 | |||
| css.properties.min-height.fit-content_function 📋 | Firefox | 8/10/2021 | 1779 | |||
| css.properties.min-inline-size.fit-content_function | Firefox | 8/10/2021 | 1779 | |||
| css.properties.min-width.fit-content_function 📋 | Firefox | 8/10/2021 | 1779 | |||
| css.properties.mix-blend-mode.plus-darker 📋 | Safari | 9/30/2015 | 3920 | |||
| css.properties.object-position.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.object-position.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.object-position.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.object-position.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset.margin-box 📋 | Safari | 9/12/2022 | 1381 | |||
| css.properties.offset.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-anchor.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-anchor.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-anchor.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-anchor.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-path.margin-box 📋 | Safari | 9/16/2024 | 646 | |||
| css.properties.offset-position.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-position.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-position.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.offset-position.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.perspective-origin.x-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.perspective-origin.x-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.perspective-origin.y-end 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.perspective-origin.y-start 📋 | Safari | 9/15/2025 | 282 | |||
| css.properties.ruby-position.alternate | Firefox | 4/19/2021 | 1892 | |||
| css.properties.speak-as 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.speak-as.digits 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.speak-as.literal-punctuation 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.speak-as.no-punctuation 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.speak-as.normal 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.speak-as.spell-out 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.stroke-color 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.stroke-color.currentColor 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.stroke-color.transparent 📋 | Safari | 4/12/2018 | 2995 | |||
| css.properties.text-align-last.match-parent 📋 | Safari | 9/12/2022 | 1381 | |||
| css.properties.text-autospace.insert 📋 | Firefox | 11/11/2025 | 225 | |||
| css.properties.text-box.cap 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box.ex 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box.ideographic 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box.ideographic-ink 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box-edge.cap 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box-edge.ex 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box-edge.ideographic 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-box-edge.ideographic-ink 📋 | Safari | 12/11/2024 | 560 | |||
| css.properties.text-decoration-inset 📋 | Firefox | 12/9/2025 | 197 | |||
| css.properties.text-decoration-inset.auto 📋 | Firefox | 12/9/2025 | 197 | |||
| css.properties.text-decoration-skip 📋 | Safari | 3/25/2019 | 2648 | 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 | 10/22/2013 | 4628 | |||
| css.properties.text-decoration-skip.none 📋 | Safari | 10/22/2013 | 4628 | |||
| css.properties.text-emphasis-position.auto | Firefox | 10/29/2024 | 603 | |||
| css.properties.white-space.preserve-spaces 📋 | Firefox | 3/19/2024 | 827 | |||
| css.properties.white-space-collapse.preserve-spaces 📋 | Firefox | 3/19/2024 | 827 | |||
| css.properties.width.fit-content_function 📋 | Firefox | 8/10/2021 | 1779 | |||
| css.selectors.-moz-first-node | Firefox | 8/8/2017 | 3242 | |||
| css.selectors.-moz-last-node | Firefox | 8/8/2017 | 3242 | |||
| css.selectors.-moz-list-bullet | Firefox | 11/9/2004 | 7897 | |||
| css.selectors.-moz-list-number | Firefox | 11/9/2004 | 7897 | |||
| css.selectors.-moz-progress-bar | Firefox | 8/16/2011 | 5426 | |||
| css.selectors.marker.counter_support 📋 | Firefox | 1/13/2026 | 162 | |||
| css.selectors.marker.quotes_support 📋 | Firefox | 1/13/2026 | 162 | |||
| css.types.image.element 📋 | Firefox | 11/14/2017 | 3144 | 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 | 12/12/2025 | 194 | |||
| css.types.random.dashed-ident 📋 | Safari | 12/12/2025 | 194 | |||
| css.types.random.element-shared 📋 | Safari | 12/12/2025 | 194 | |||
| css.types.random.step 📋 | Safari | 12/12/2025 | 194 | |||
| css.types.ratio.number_value | Firefox | 6/30/2020 | 2185 |