It ebbs and flows over time. All browsers will be attempting to improve performance, but at the same time adding features. More features often impact performance negatively.

Most normal pages are apparently faster in Firefox right now, but Google might make an optimisation effort in chromium that might make Firefox comparatively slower.

The main pages that are still slower in Firefox are Google sites. Google has repeatedly made things on their pages that unfairly favor Chrome. For example at one point they added an invisible frame that had no functionality over the video player on YouTube. They obviously made optimisations in chrome at the same time so they wouldn’t be affected, but Firefox’ hardware acceleration of videos broke, because the video now had additional items over top that it needed to custom handle. This gave chrome a massive performance edge on YouTube, until Firefox started ignoring completely invisible overlays of videos, just like Chrome did