Mozilla Firefox has just shipped support for Interaction to Next Paint (INP), one of Google’s Core Web Vitals metrics focused on responsiveness. This is great news for anyone monitoring site speed and user experience.
At RUMvision, our Core Web Vitals monitoring is powered by Google’s official web-vitals.js library. This means any browser that supports a Core Web Vital or underlying APIs will automatically be tracked in RUMvision.
Firefox allows INP tracking
Technically speaking, Firefox doesn't directly expose INP itself. It supports PerformanceEventTiming.interactionId, which is enabled by default in Firefox 144.
With this information, developers or libraries can group interactions (e.g. pointerdown, click) and measure whatever they like. For example, the INP metric. Before this, each event had to be measured separately, which made it hard to connect related events as part of the same interaction.
Firefox release notes
The good news is that Firefox 144 was released today, October 14th. In their release notes, Firefox covers their INP support as following:
Firefox now supports PerformanceEventTiming.interactionId, allowing developers to group related input events. This enables support for the Interaction to Next Paint (INP) responsiveness metric.
INP data from Firefox
With the web-vitals.js library being able to collect INP on behalf of Firefox users, we’re already seeing the metric show up in our raw data. See the chart below depicting INP events coming from Firefox browsers, where we can see an uptick as of 3PM GMT+2.
Why this matters
INP is one of the newer Core Web Vitals metrics, focused on responsiveness. Having Firefox adopt the underlying API means:
- More coverage across browsers
We can measure real user experience more consistently. - Better insight for site owners
Especially if an above average portion of your traffic comes from Firefox desktop users. - Immediate visibility in RUMvision
No extra setup, no extra cost.
Real User Monitoring data
A couple of practical things to keep in mind when looking at your Real User Monitoring data:
- Firefox users are still mostly on desktop.
- The share of Firefox visitors varies widely depending on your website and audience. Some site owners will see relatively more INP events coming from Firefox than others.
- With RUMvision, you’re not paying extra for this data — it’s included.
CrUX and SEO
Google uses Core Web Vitals data from the Chrome User Experience Report (CrUX) for its Page Experience ranking that is part of Google SEO. However, CrUX data continues to be collected from Google Chrome users only.
Even though these metrics don’t flow into CrUX, support in Firefox and Safari is still valuable for getting a more complete view of real user experience across all browsers.
This also means that differences between various site speed tools may become more noticeable. Most RUM tools let you segment data, so you can focus on what matters most — whether that’s SEO, UX, or both.
Core Web Vitals interop
Firefox adding support for INP means we're a step closer to the long-awaited interoperability effort.
New to interop and/or invested in full browser support for performance metrics and APIs? Read our Interop 2026 blogpost.
Here’s how browser support for Core Web Vitals looks right now:
Largest Contentful Paint
Google Chrome was the first to support the Largest Contentful Paint (LCP) metric back in September 2019, followed by other Chromium browsers.
Firefox added support for LCP back in January 2024 since version 122, after announcing it at the yearly performance.now conference in 2023.
At time of writing, support from Safari even became part of Safari Technology Preview 230 (update: now in Safari 26.2 beta).
Limited availability
Largest contentful paint (LCP) is not Baseline because it does not work in some of the most widely-used browsers.
- Only supported in Chrome 77, Edge 79 and Firefox 122
- Continue reading about largest contentful paint
Register to RUMvision to see more resources and learn if your website visitors would already benefit from this feature today.
Interaction to Next Paint
Interaction to Next Paint (INP) is a derived metric calculated from the Event Timing API.
Chromium started exposing interactionId´s since November 2021. While Firefox already supported the Event Timing API since June 2021, it didn´t expose interactionId´s yet. As of today, it does.
At time of writing, Safari doesn’t yet support the Event Timing API. But that is about to change as it was released in Safari Tech Preview 279 and already spotted in 277 by Barry Pollard (update: now in Safari 26.2 beta).
The Baseline badge below should reflect any changes to always show up-to-date support.
Limited availability
Event timing is not Baseline because it does not work in some of the most widely-used browsers.
- Only supported in Chrome 76, Edge 79 and Firefox 89
- Continue reading about event timing
Register to RUMvision to see more resources and learn if your website visitors would already benefit from this feature today.
Cumulative Layout Shift
To be able to measure the Cumulative Layout Shift (CLS) metric, the Layout Instability API is needed. At time of writing, this is a Chromium only API. Based on how browsers render pages, it is not expected to be supported by other browsers any time soon.
This means that for now, we have to rely on Chromium browsers to detect and prevent user frustration caused by layout shifts. And hope we are fixing it for users on other browsers too.
Limited availability
Layout instability is not Baseline because it does not work in some of the most widely-used browsers.
- Only supported in Chrome 84 and Edge 84
- Continue reading about layout instability
Register to RUMvision to see more resources and learn if your website visitors would already benefit from this feature today.
Looking ahead
Browser support for Core Web Vitals is steadily improving, which means more reliable data for developers and site owners. And a wider view on your real users and their experiences.
If you’re already using RUMvision for site speed monitoring, you should notice an uptick in INP data coming from your Firefox users. Not yet tracking Core Web Vitals with real user monitoring? Get started with RUMvision today.
