What Changed in Gecko: Firefox 131
GeckoView EngineWhy This Matters
Gecko is the last truly independent browser engine — the only major alternative to Google’s Blink. Every Firefox release ripples through Tor Browser, LibreWolf, Mullvad Browser, and dozens of other privacy-focused forks. When Gecko ships a new JavaScript API or tightens cookie policy, it’s not just Firefox users who benefit — it’s the entire ecosystem that depends on engine diversity for a healthier web.
Firefox 131 is a significant release: Iterator helpers land for JavaScript, Text Fragments arrive for linking to specific page content, and CHIPS brings partitioned cookies to Gecko. Here’s the full breakdown.
JavaScript
The headline feature is Iterator helper methods — a suite of 10 new prototype methods including .map(), .filter(), .reduce(), .find(), .take(), and .drop(). These bring Array-like chainable operations directly to iterators, eliminating the need to create intermediate arrays. For large datasets that can’t fit in memory as an array, this is transformative.
WebAssembly exception handling also improved: the new exnref value type enables cleaner exception propagation between Wasm and JavaScript in both directions (bug 1908375).
CSS
CSS changes in 131 are modest but forward-looking. The inset-area property has been renamed to position-area as part of the evolving Anchor Positioning specification (bug 1909358). While anchor positioning itself remains behind a preference flag, this rename signals that Mozilla is actively tracking the spec and preparing for full implementation.
Web APIs
Text Fragments are the standout API addition. Users and developers can now link directly to specific text on a page using a special URL fragment syntax — the same feature Chrome shipped years ago. Firefox also adds the Document.fragmentDirective property for feature detection and the ::target-text CSS pseudo-element for styling highlighted fragments (bug 1914877).
The PointerEvent interface gained altitudeAngle and azimuthAngle properties, giving stylus and pen input more precise spatial data (bug 1656377).
The caretPositionFromPoint() method now supports Shadow DOM — pass a ShadowRoot to get accurate caret positions inside web components (bug 1914596).
Security & Privacy
Firefox 131 tightens cookie security in two ways. First, SameSite=None cookies now require the Secure attribute — if you’re setting cross-site cookies over plain HTTP, they’ll be rejected (bug 1909673). Since Firefox treats cookies without an explicit SameSite value as SameSite=None, this effectively pushes all ambiguous cookies toward HTTPS.
Second, Cookies Having Independent Partitioned State (CHIPS) is now supported. The Partitioned directive on Set-Cookie lets developers opt cookies into per-top-level-site storage — enabling legitimate third-party use cases (embedded widgets, chat tools) while blocking cross-site tracking (bug 1908160).
Developer Tools
No major DevTools-specific features shipped in 131, but WebDriver BiDi saw improvements: the network.continueResponse command now supports cookies, headers, status codes, and reason phrases (bug 1853887), and keyUp/keyDown actions no longer accept multiple characters (bug 1910352).
Performance
Temporary permissions are a subtle UX improvement that reduces permission fatigue: when you grant a site access to geolocation or camera, Firefox now offers to make it temporary — expiring after 1 hour or when the tab closes. Less permission clutter means less surface area for abuse.
For Linux users, HiDPI font scaling now fully respects GNOME 3/GTK3 settings, resolving long-standing inconsistencies on high-resolution displays.
Bottom Line
Front-end developers benefit most from Iterator helpers and Text Fragments — two features that close long-standing gaps with Chromium. Privacy-conscious users get stronger cookie defaults with CHIPS and mandatory Secure on cross-site cookies. Stylus and pen users get better input precision. And the entire Gecko ecosystem — Tor, LibreWolf, Mullvad — inherits all of it.