Verify and update Firefox feature flag data#30012
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The `dom.serviceWorkers.navigationPreload.enabled` flag was enabled by default in Firefox 99 (bug 1754786); the header no longer requires a flag.
…x 144 The `dom.viewTransitions.enabled` flag was enabled by default in Firefox 144 (bug 1985809), matching the parent `startViewTransition` method.
`dom.webshare.enabled` is enabled by default only in Nightly and early Beta (`@IS_EARLY_BETA_OR_EARLIER@`), so `Navigator.share`/`canShare` (and their text-data parameters) are marked `preview` on desktop Firefox.
`layout.css.attr.enabled` is enabled by default only in Nightly (`@IS_NIGHTLY_BUILD@`), so the `attr()` type function and its data types are marked `preview`.
`layout.css.scroll-driven-animations.enabled` is enabled by default only in Nightly (`@IS_NIGHTLY_BUILD@`), so named-range keyframes and the `scroll` timeline range name are marked `preview`.
`layout.css.text-box.enabled` is enabled by default only in Nightly (`@IS_NIGHTLY_BUILD@`), so the `text-edge` data type values are marked `preview`.
`network.cookie.sameSite.schemeful` is enabled by default only in Nightly (`@IS_NIGHTLY_BUILD@`), so schemeful `SameSite` is marked `preview`.
`Permissions.revoke()` shipped in Firefox 47-50, then required the `dom.permissions.revoke.enable` flag from 51. That pref no longer exists in Firefox, so drop the defunct flag statement and keep the 47-51 range.
`:-moz-submit-invalid` shipped in Firefox 4-87, then required the `layout.css.moz-submit-invalid.enabled` flag from 88. That pref no longer exists, so drop the defunct flag statement and keep the 4-88 range, matching Firefox for Android.
The `dom.screenBrightnessProperty.enabled` and `dom.screenEnabledProperty.enabled` flags no longer exist in Firefox. These non-standard B2G-era properties were never implemented in any browser without a flag, so remove both features.
The `layout.css.element-content-none.enabled` flag no longer exists in Firefox; `content: none` now resolves to `normal` on non-pseudo elements (bug 1725208 is unresolved). It never shipped unflagged in any browser, so remove the feature.
The `layout.css.heading-selector.enabled` flag no longer exists in Firefox. Mark `:heading` unsupported (still supported in Safari 27), and remove `:heading()`, which was never implemented in any browser without a flag.
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caugner
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Jul 9, 2026
| "firefox": { | ||
| "version_added": "117", | ||
| "partial_implementation": true, | ||
| "notes": "Supported on Windows since Firefox 117 and on Linux since Firefox 137. On macOS, only available in Nightly builds." |
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Should keep the same approach as before, with two statements.
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Summary
Verify every Firefox
flagsentry listed in #30010 against current Gecko source and update the affected features. Each pref was checked withsearchfox-cli, and versions confirmed via Bugzilla target milestones.Test results and supporting details
Prefs verified against
github.com/mozilla-firefox/firefox(gecko-devis archived) and searchfoxmozilla-central(Nightly 154),mozilla-release(152), andmozilla-esr*.npm run lint api css httppasses; the only remainingFlag datalinter exception isapi.Window.dump(intentional).Enabled by default in release → drop flag, record shipped version
dom.serviceWorkers.navigationPreload.enabledhttp.headers.Service-Worker-Navigation-Preload:97+ flag →99. Enabled by default in Firefox 99 (bug 1754786); pref now defaultstrue.dom.viewTransitions.enabledapi.Document.startViewTransition.updateCallback_parameter:140+ flag →144, matching the parent method. Enabled by default in Firefox 144 (bug 1985809); pref now defaultstrue.dom.webnotifications.requireinteraction.enabledapi.Notification.requireInteraction: →117,partial_implementation, flag dropped. Enabled by default on Windows since 117 (bug 1794475) and Linux since 137 (bug 1947738); macOS remains Nightly-only. Also removes the now-unnecessaryFlag datalinter exception. Pref block:#if XP_WIN || XP_LINUX → true, else@IS_NIGHTLY_BUILD@.Enabled by default only in Nightly →
previewdom.webshare.enabledapi.Navigator.share,.canShare(+ text-data parameters): →preview. Pref defaults@IS_EARLY_BETA_OR_EARLIER@— off in release, on in Nightly (desktop).layout.css.attr.enabledcss.types.attr.*(16 features): →preview. Pref defaults@IS_NIGHTLY_BUILD@.layout.css.scroll-driven-animations.enabledcss.at-rules.keyframes.named_range_keyframes,css.types.timeline-range-name.scroll: →preview. Pref defaults@IS_NIGHTLY_BUILD@.layout.css.text-box.enabledcss.types.text-edge.*(5 features): →preview(partial_implementation/notes retained). Pref defaults@IS_NIGHTLY_BUILD@.network.cookie.sameSite.schemefulhttp.headers.Set-Cookie.SameSite.schemeful: →preview. Pref defaults@IS_NIGHTLY_BUILD@.Pref removed → drop defunct flag or remove feature
dom.permissions.revoke.enableapi.Permissions.revoke: dropped the defunct flag statement, keeping the historical47–51range (shipped 47–50, flag-only from 51). Pref no longer in mozilla-central.layout.css.moz-submit-invalid.enabledcss.selectors.-moz-submit-invalid: dropped the defunct flag statement, keeping4–88(shipped 4–87, placed behind the flag in 88 per bug 1694129). Pref no longer in mozilla-central.layout.css.heading-selector.enabledcss.selectors.heading→false(still supported in Safari 27);css.selectors.headingfunctionremoved (never implemented in any browser). Pref never existed / not in mozilla-central.dom.screenBrightnessProperty.enabled&dom.screenEnabledProperty.enabledapi.Screen.mozBrightnessandapi.Screen.mozEnabled: removed (non-standard B2G-era properties, never shipped unflagged; combined into one commit as the hook can't commit one while the other still carries a flag). Prefs no longer in mozilla-central.layout.css.element-content-none.enabledcss.properties.content.none_applies_to_elements: removed. Implemented behind the flag in 91 (bug 1699964), butcontent: nonenow resolves tonormalon non-pseudo elements and the spec question is unresolved (bug 1725208); the pref was removed after Firefox 115 (present in esr115, absent in current mozilla-central).Additional notes
Deliberately left unchanged — the flag is still required in shipped Firefox:
browser.dom.window.dump.enabledapi.Window.dump: pref defaults@IS_NOT_MOZILLA_OFFICIAL@, i.e. off in every official build including Nightly.dump()is always exposed but is a runtime no-op unless enabled.network.cors_preflight.authorization_covered_by_wildcardhttp.headers.Access-Control-Allow-Headers.authorization_not_covered_by_wildcard: the feature requires setting the pref tofalse, but it defaults totrue, so the flag is still needed.Related issues
Part of #30010.