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 |
|---|---|---|---|---|---|---|
| html.elements.a.attributionsourceid 📋 | Safari | 4/26/2021 | 1788 | |||
| html.elements.iframe.allow.document-domain 📋 | Firefox | 3/10/2020 | 2200 | |||
| html.elements.iframe.allow.gamepad 📋 | Firefox | 8/10/2021 | 1682 | 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 📋 | Firefox | 8/1/2023 | 961 | Firefox for Android: Not available due to a limitation in Android (see bug 1473346). | ||
| html.elements.input.alpha 📋 | Safari | 3/31/2025 | 353 | |||
| html.elements.input.colorspace 📋 | Safari | 3/31/2025 | 353 | |||
| html.elements.input.switch | Safari | 3/5/2024 | 744 | |||
| html.elements.script.type.speculationrules 📋 | Safari | 12/12/2025 | 97 | 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 | 12/12/2025 | 97 | 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 | 12/12/2025 | 97 | |||
| html.elements.script.type.speculationrules.referrer_policy 📋 | Safari | 12/12/2025 | 97 | |||
| html.elements.script.type.speculationrules.relative_to 📋 | Safari | 12/12/2025 | 97 | |||
| html.elements.script.type.speculationrules.source_optional 📋 | Safari | 12/12/2025 | 97 | |||
| html.elements.script.type.speculationrules.tag 📋 | Safari | 12/12/2025 | 97 | |||
| html.elements.script.type.speculationrules.urls 📋 | Safari | 12/12/2025 | 97 | |||
| html.elements.script.type.speculationrules.where 📋 | Safari | 12/12/2025 | 97 | |||
| html.elements.template.shadowrootreferencetarget | Safari | 9/15/2025 | Firefox | 3/24/2026 | 190 |