LCP & INP Coming to Safari & Firefox in 2025: What It Means for Your Platform
For years, performance tracking has been incomplete—relying largely on Google Chrome data. But that’s about to change.
At Interop 2025, an annual collaboration between major browser vendors to improve web standardization efforts, it was announced that Safari and Firefox will finally support measuring of two key Core Web Vitals natively: Largest Contentful Paint (LCP) and Interaction to Next Paint (INP).
Until now, users optimizing for speed have struggled with blind spots in how their platforms perform for Safari and Firefox users. This update means a complete cross-browser view of real-world performance—enabling smarter optimizations, better user experiences, and more informed decision-making.
Understanding Core Web Vitals
Core Web Vitals are a set of metrics introduced by Google to measure real-world user experience on the web, focusing on key aspects of page performance:
- Largest Contentful Paint (LCP): Measures loading performance by tracking the time it takes for the largest content element to become visible within the viewport. An ideal LCP occurs within 2.5 seconds of when the page first starts loading.
- Interaction to Next Paint (INP): Assesses page responsiveness by measuring the time from a user interaction (like a click or tap) to the next frame being painted. A good INP is under 200 milliseconds.
- Cumulative Layout Shift (CLS): Evaluates visual stability by quantifying how much the page layout shifts unexpectedly during the lifespan of the page. A CLS score of less than 0.1 ensures a stable visual experience.
⚠️ While LCP and INP are now being adopted by Safari and Firefox, it’s important to note that Cumulative Layout Shift (CLS) monitoring was not within the scope of Interop 2025 and remains unsupported natively in these browsers.
Why This Matters
A Full Picture of Performance
If you’ve been relying on Chrome-based data to measure platform speed, you’ve only seen part of the picture. With LCP and INP now natively trackable in Safari and Firefox, you will soon be able to monitor performance across more major browsers—ensuring optimizations benefit your entire audience.
Better Conversions & Engagement
Faster platforms drive more revenue. LCP and INP in Safari and Firefox allow you to track load times and responsiveness for all users—not just those on Chrome. The result? Higher engagement, lower bounce rates, and increased conversions across the board.
Smarter SEO & Marketing Decisions
Google’s rankings are still based on Chrome’s Core Web Vitals, but this update gives marketers a more complete dataset to fine-tune performance, optimize UX, and boost campaign effectiveness across all major browsers.
What’s Next?
This shift marks a major step toward a unified web performance standard. With LCP and INP expanding beyond Chrome, we could soon see:
- More accurate industry benchmarks that reflect real-world performance across browsers.
- Advanced real-user monitoring (RUM), providing more granular performance insights.
- Potential SEO changes if search engines eventually incorporate multi-browser performance data.
How to Get Ready
✅ Enable Real User Monitoring (RUM) for Safari and Firefox data.
🚫 Don’t rely solely on PageSpeed Insights (PSI) or CrUX—they still only track Chrome.
🔍 Analyze LCP & INP across all browsers to uncover hidden performance gaps.
🚀 Experiment with modern optimizations like the Speculation Rules API and View Transitions API.
The Bottom Line
This is a major milestone for web performance. For the first time, you can track platform speed and responsiveness natively across all major browsers. More complete data means better decisions, smoother user experiences, and higher conversions.
