At Interop 2025, a major cross-browser initiative led by Google, Apple, Mozilla, and other industry leaders, an exciting announcement was made: Safari and Firefox will finally support two key web performance metrics: 

✅ Largest Contentful Paint (LCP)  

✅ Interaction to Next Paint (INP)

For businesses, this is a game-changer: they’ll finally get the full picture of how their site performs for all visitors, making it easier to plan smarter optimizations.

The problem: A fragmented view of performance

For years, businesses optimizing their websites for speed have had a blind spot: performance data was largely driven by Chrome users.

Why?

Safari and Firefox never exposed LCP and INP, two critical Core Web Vitals that measure how fast a page loads and how responsive it feels. This meant that:

• Real-user monitoring (RUM) solutions were mostly relying on Chrome data, creating an incomplete picture.

• Businesses were making site speed decisions based on only a subset of their audience, ignoring performance issues that may have existed for millions of Safari and Firefox users.

• Marketers and SEO specialists lacked full-funnel visibility into how different browsers affected bounce rates, engagement, and conversions.

This data gap meant businesses were unknowingly losing potential customers due to performance issues they couldn’t even track.

A push from the performance community

For years, the web performance community has advocated for better tracking across all browsers. While Chrome provided data on key Core Web Vitals, Safari and Firefox lacked support for LCP and INP, making it difficult to get a complete picture of how websites performed across different browsers.

One solution developed to bridge this gap is a free polyfill that enabled INP measurement in Safari and Firefox before native support was available. By simulating missing PerformanceEventTiming events, it provided a way to track responsiveness more consistently across browsers.

👉 Want to track INP on Safari and Firefox before native support rolls out? Use our free polyfill to start collecting data today.

With Safari and Firefox now adding official support for these metrics, this workaround will soon no longer be necessary. This update moves the industry toward a more complete, multi-browser understanding of web performance, giving businesses more reliable insights and better opportunities to optimize their sites for all users.

Why this matters for your business

1. A full picture of your customer's experience

If you’ve been optimizing for page speed, chances are, you’ve only been seeing Chrome’s side of the story. But with LCP and INP soon available in Safari and Firefox, you’ll finally have data on how your website performs for ALL users, not just Chrome users.

2. Faster sites mean higher conversions

Every second of delay costs you sales. LCP in Firefox and Safari will let you measure exactly how long it takes for your most important content to load across all browsers. And with INP tracking in Safari and Firefox, you’ll also know how responsive your site feels to user interactions like clicks and taps.

3. Smarter SEO & marketing decisions (but not in the way you might think)

Google already uses Core Web Vitals like LCP and INP as part of its ranking factors, but only based on CrUX (Chrome User Experience Report) data which means rankings are influenced solely by Chrome users’ experiences, not Safari or Firefox.

So, while LCP and INP in Safari and Firefox won’t directly impact Google rankings, they will still be a game-changer for marketers. With this new data, businesses can:

• Optimize for a complete dataset across all major browsers (not just Chrome).

• Fine-tune site speed and responsiveness for more users, leading to better engagement and retention.

• Improve ad performance and lower bounce rates by ensuring fast, smooth experiences across Safari and Firefox.

Will Google ever use Safari & Firefox data for rankings?

Right now, there’s no official confirmation that Google will include performance data from non-Chrome browsers in its ranking algorithm. Since CrUX is based on Chrome experiences, that’s what determines rankings for now.

However, as the web ecosystem pushes for a more browser-agnostic approach to performance measurement, it’s possible that Google could evolve its approach in the future.

What’s next? The future of web performance data

With Safari and Firefox stepping up their tracking game, this opens up several possibilities for the future:

🚀 More accurate industry benchmarks:
Right now, industry-wide performance benchmarks are heavily skewed toward Chrome’s user base. As LCP and INP in Safari and Firefox become widely available, businesses and researchers will get a more balanced dataset leading to better best practices for web speed optimization.

📊 More advanced RUM analytics:
With real user monitoring (RUM) tools soon being able to capture Safari and Firefox data, businesses will have more granular insights into how different browsers perform under real-world conditions. This could lead to more sophisticated AI-driven optimizations based on complete datasets.

🔍 Potential future SEO changes:
Google isn’t pulling Safari and Firefox performance data into rankings - yet. But as pressure builds for a more holistic approach to Core Web Vitals, we might see changes in how search engines evaluate page speed and UX across different browsers.

🤝 Cross-browser collaboration on web standards:
Interop 2025 is a clear sign that browsers are working together to create a more unified web experience. If this trend continues, we might see even more standardization in performance tracking, benefiting businesses that invest in speed optimization today.

Beyond LCP and INP support, recent advancements like the Speculation Rules API and View Transitions API, currently supported only in Chrome, highlight how browsers are exploring ways to make the web feel faster and smoother. These technologies allow for preloading future pages based on user behavior and seamless visual transitions between pages, reducing perceived load times and improving engagement.

Could Safari and Firefox adopt these innovations in the future? Given the push for more cross-browser consistency, it’s possible we’ll see wider adoption of these performance-enhancing APIs. If that happens, businesses already leveraging them in Chrome will be well-positioned to benefit when support expands.

How to get your site ready for LCP & INP in Safari and Firefox

With Safari and Firefox adding support for LCP and INP, businesses have a new opportunity to improve performance tracking and optimization. Here’s how to stay ahead:

✅ Start collecting data across all browsers: Real User Monitoring (RUM) solutions will soon be able to track LCP and INP in Safari and Firefox, giving you a fuller picture of real-world performance. Make sure your analytics setup can capture these metrics.

🚫 Don’t rely solely on PageSpeed Insights (PSI) or CrUX: Google’s tools only reflect Chrome users' experiences, so relying on them alone means you’ll miss key performance data from Safari and Firefox users.

🔍 Adopt a RUM-based analytics solution: To get the most accurate insights, use a performance monitoring tool that tracks real-world data across all major browsers, not just Chrome.

🚀 Stay ahead of future optimizations: While Speculation Rules API and View Transitions API are currently Chrome-only, their potential for Safari and Firefox in the future makes them worth exploring now. Implement them where possible so you’re ready if cross-browser support expands.

By adapting now, you’ll ensure your site delivers faster load times, better engagement, and a more seamless experience, for all users, across all browsers.

The bottom line

This is a game-changer for website performance optimization. With Safari and Firefox now supporting LCP and INP, businesses can finally optimize their web experience for all users. More complete data means better decisions, a smoother UX, and ultimately, higher conversions.

If your business depends on website speed and engagement (spoiler: it does), these changes are too important to ignore.

FAQ

1. What did Interop 2025 announce about LCP and INP?

At Interop 2025, it was announced that Safari and Firefox will support LCP and INP, aligning with Chrome to offer better web performance tracking across all major browsers.

2. How will this impact website performance tracking?

• More accurate real-user monitoring (RUM) across Safari, Firefox, and Chrome.

• Better optimization decisions with a complete dataset from all browsers.

• Stronger user engagement as businesses fix performance issues for all visitors, not just Chrome users.

3. Will LCP and INP in Safari and Firefox affect SEO rankings?

No, not yet. Google’s ranking algorithm still relies on CrUX (Chrome User Experience Report), which excludes Safari and Firefox data. However, as web performance measurement becomes more browser-inclusive, this could change in the future.

4. How can I start tracking INP in Safari and Firefox before native support?

You can use our free polyfill to measure INP in Safari and Firefox today, simulating the missing PerformanceEventTiming events.

👉 Try our free polyfill

5.What steps should I take to prepare my site?

✅ Enable Real User Monitoring (RUM) to collect LCP and INP data from all browsers.
🚫 Don’t rely only on PageSpeed Insights (PSI) or CrUX, as they only reflect Chrome user data.
🔍 Analyze LCP and INP in Chrome to identify and fix potential bottlenecks.
🚀 Experiment with modern optimizations like Speculation Rules API and View Transitions API, currently Chrome-only, but potentially expanding to Safari and Firefox in the future.

6.What’s next for web performance?

• More accurate industry benchmarks with multi-browser data.

• Advanced real-user monitoring (RUM) solutions for cross-browser insights.

• Potential future SEO updates as Google evaluates broader performance data.

• Stronger cross-browser collaboration, potentially bringing Speculation Rules API and View Transitions API to Safari and Firefox.