A few changes are being rolled out that may impact loading metrics, such as FCP and LCP. Most of these changes are browser optimizations that should improve those loading metrics for everyone.
We also improved the accuracy of the timeOrigin value, on which all loading
metrics are based. It now takes into account an extra IPC call that happens
before beforeUnload event handlers.
In scenarios where traffic to your site is coming from a site with a
beforeUnload handler, your timeline metrics are likely to slightly change:
because the timeOrigin value is now earlier, durations relative to
timeOrigin will appear to be larger.
Note that the duration of the beforeUnload event itself is not included in
the timeOrigin, as its semantic meaning is not changed.
On the whole, users will see significant improvements to both FCP and LCP due to this effort.
The pre-beforeUnload IPC change means that if large parts of the traffic to
your site are coming from sites with a beforeUnload handler, you may see a
mix of metric regressions and progressions.
Otherwise, you're likely to see your metrics improve.
This change is being rolled out starting from Chrome 99.