--- title: Firefox 155 and Chrome's new two-week release cycle:... description: Firefox and Chrome are both shifting to two-week major release cycles, with Firefox 155 landing as the first release under the new schedule. Firefox 155 ships... canonical: https://daily.dev/posts/firefox-155-and-chrome-s-new-two-week-release-cycle-what-changes-for-users-and-developers-vbmwzw0q8 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Firefox 155 and Chrome's new two-week release cycle: what changes for users and developers | daily.dev og:description: Firefox and Chrome are both shifting to two-week major release cycles, with Firefox 155 landing as the first release under the new schedule. Firefox 155 ships... og:url: https://daily.dev/posts/firefox-155-and-chrome-s-new-two-week-release-cycle-what-changes-for-users-and-developers-vbmwzw0q8 og:image: https://api.daily.dev/og/posts/vbMwzw0q8.png og:image:alt: Firefox 155 and Chrome's new two-week release cycle: what changes for users and developers og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Firefox 155 and Chrome's new two-week release cycle: what changes for users and developers **[Collections](https://daily.dev/sources/collections)** · 4 min read · 0 upvotes · 0 comments ## Summary Firefox and Chrome are both shifting to two-week major release cycles, with Firefox 155 landing as the first release under the new schedule. Firefox 155 ships Happy Eyeballs v3 (racing HTTP/2 vs HTTP/3 and IPv4 vs IPv6 simultaneously using HTTPS DNS records), QUIC v2 support, an opt-in AI browsing mode called Smart Window (US/Canada/France only), plus various developer-facing CSS and DevTools additions. The faster release cadence creates practical issues for RUM: browser-version cohorts shrink faster, multiple versions can land in a single reporting window, and percentile shifts may reflect population changes rather than regressions. Recommended mitigations include minimum sample thresholds, aligning release dates with a deployment change calendar, and using Beta windows to test instrumentation. Separately, Chrome 152 DevTools now shows Core Web Vitals for soft navigations, and a large dataset analysis surfaced a large 'Unattributed Navigation Overhead' portion of TTFB not explained by standard phases. ## Content Firefox 155 is out, and it's the first release under Mozilla's new twice-monthly cadence - major versions now ship every two weeks, matching Chrome's pace since version 153. ## Faster connections The headline networking change is Happy Eyeballs v3. Where previous versions tried IPv4 and IPv6 connections in sequence, v3 now races multiple paths simultaneously - IPv4, IPv6, HTTP/2, and HTTP/3 - using modern DNS records to pick whichever responds first. In practice this should cut the time you spend staring at a loading spinner when one protocol is slow or broken. Firefox 155 also adds QUIC v2 support for HTTP/3. When a server supports it, Firefox can switch QUIC versions without an extra round trip, which matters most on flaky mobile connections. ## Built-in ad blocker on iOS Mozilla shipped a built-in content blocker for Firefox on iOS, built on Apple's WebKit content blocker API and using the EasyList filter list. It's off by default. The caveats are real: it can't block ads served directly by the site, search ad results, or Mozilla's own sponsored shortcuts. Firefox is late here - Brave, Opera, and Vivaldi have had similar blocking on iOS for years. The deeper story is that Apple's BrowserEngineKit, opened in March 2024 under the EU's Digital Markets Act to let rival browser engines run on iPhones, still has no actual adopters two and a half years later. Google and Mozilla have both prototyped alternative engines but haven't shipped them. Microsoft measured a Blink prototype running 28.6% faster than WebKit on Speedometer 3.1. Open Web Advocacy is pushing the European Commission to intervene. ## AI features with a master off switch Firefox is rolling out granular AI controls. Individual features - translations, alt text generation, tab group suggestions, link preview summaries - can each be toggled independently. There's also a single master switch that disables all current and future AI features at once, which is a more honest approach than burying things in settings. For users who want AI features, the built-in sidebar now lets you pick from Claude, ChatGPT, Gemini, or Le Chat Mistral rather than being locked into one provider. Smart Window, the AI-powered browsing mode that uses open tabs and browsing history as context for summaries and comparisons, is now available in the US, Canada, and France (English only, still in beta). This release adds tab grouping, visual history previews, and a new integration with Exa for sourced web answers. ## Other changes - Tracker block count now shows in the address bar - Container tabs can be reordered - `mailto:` links now only open from explicit user actions - Urdu and Marathi translation support added - PDF scaling above 100% now works - Linux: fixed a bug that prevented sleep, and disappearing text in web apps - Windows: Nintendo Switch Pro controller support in web games via Nvidia's GeForce NOW work ## For developers - CSS `attr()` now works on all properties - New `alpha()` color function - New `font-width` CSS property - `progress()` CSS function - CSS nesting limits for blocks and functions - WebAssembly Compact Import Section and Wide Arithmetic - Improved WebRTC interoperability - `Promise.allKeyed` - DevTools can now emulate `prefers-reduced-motion` ## Network admin note The captive portal detection domain changed from `detectportal.firefox.com` to `firefox-portal-detection.com`. If you manage a network with an allow list, you'll need to add the new domain. ## A note on RUM and release cadence The shift to two-week releases has a subtle effect on performance monitoring. Browser version is now a more volatile dimension in real user monitoring data - exact-version cohorts shrink faster, and multiple browser milestones can land inside a single reporting window. A percentile movement in your RUM data might reflect a population shift rather than a product regression. Worth pulling browser release dates into the same calendar as your application deploys and CDN changes, and treating them as annotations rather than adoption claims. ## Questions this post answers ### What is Happy Eyeballs v3 in Firefox 155? Happy Eyeballs v3 is a networking algorithm in Firefox 155 that races HTTP/2 and HTTP/3 connections alongside IPv4 and IPv6 options simultaneously, using HTTPS DNS resource records to determine which paths are available. This lets Firefox settle on the fastest connection without waiting for slower options to time out, extending the original IPv4/IPv6 racing approach. _Track networking changes like this on daily.dev before they affect your site's connection performance._ ### Why did Chrome and Firefox switch to a two-week release cycle? Chrome and Firefox both moved to two-week major release cycles, with Chrome 153 hitting Stable on September 8 and Firefox 155 landing September 1 as the first release under Mozilla's new twice-monthly schedule. For real user monitoring, this shortens browser-version cohort lifespans, increases noise in percentiles, and can cause multiple versions to land within a single reporting window. _Developers tracking RUM data reliability follow release cadence shifts like this on daily.dev._ ### How can I stop browser version upgrades from skewing my RUM percentile data? Set minimum sample thresholds before trusting any browser-version segment, since cohorts with only a few hundred sessions produce noisy percentiles. Also pull browser release dates into the same change calendar used for deployments and CDN changes, treating them as chart annotations rather than adoption claims, and use the three-week Beta window before Stable releases to validate instrumentation. _Anyone maintaining RUM dashboards can follow browser release timing on daily.dev to catch data shifts early._ --- Tags: [#webdev](https://daily.dev/tags/webdev), [#google-chrome](https://daily.dev/tags/google-chrome), [#firefox](https://daily.dev/tags/firefox) [View this post on daily.dev](https://daily.dev/posts/firefox-155-and-chrome-s-new-two-week-release-cycle-what-changes-for-users-and-developers-vbmwzw0q8) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Firefox 155 and Chrome's new two-week release cycle: what changes for users and developers","url":"https://daily.dev/posts/firefox-155-and-chrome-s-new-two-week-release-cycle-what-changes-for-users-and-developers-vbmwzw0q8","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/firefox-155-and-chrome-s-new-two-week-release-cycle-what-changes-for-users-and-developers-vbmwzw0q8"},"datePublished":"2026-09-01T03:52:09.935Z","dateModified":"2026-09-02T13:12:39.338Z","description":"Firefox and Chrome are both shifting to two-week major release cycles, with Firefox 155 landing as the first release under the new schedule. 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This lets Firefox settle on the fastest connection without waiting for slower options to time out, extending the original IPv4/IPv6 racing approach. Track networking changes like this on daily.dev before they affect your site's connection performance."}},{"@type":"Question","name":"Why did Chrome and Firefox switch to a two-week release cycle?","acceptedAnswer":{"@type":"Answer","text":"Chrome and Firefox both moved to two-week major release cycles, with Chrome 153 hitting Stable on September 8 and Firefox 155 landing September 1 as the first release under Mozilla's new twice-monthly schedule. For real user monitoring, this shortens browser-version cohort lifespans, increases noise in percentiles, and can cause multiple versions to land within a single reporting window. 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