I have the Web Vitals chrome extension
installed on my browser and I've noticed LCP increases on pages I open in the background.
If I open a page in a new tab in the background, but I don't navigate to the page right away, the time elapsed between clicking on the page URL and actually visiting the tab is added to the LCP.
E.g., I'm viewing /page-a/ and open /page-b/ in the background in a new tab. I wait 90 seconds before navigating to the tab, and the extension reports my local LCP time as 92 seconds. If I open the page in the same tab it reports 2 seconds to LCP.
The extension does not report on FCP but I would guess it's impacted in a similar way.
The description in the Chrome Web Store says, "This extension measures the Core Web Vitals ... [and] is consistent with how these metrics are measured by Chrome and reported to other Google tools (e.g. Chrome User Experience Report, Page Speed Insights, Search Console)."
This would lead me to believe that the inflated LCP is in fact recorded and used by Google as part of the PX ranking factor.
If that assumption is correct, then isn't this a gross misrepresentation of CWV in those situations, and should be fixed to only start measuring FCP and LCP when the page is actually in view of the browser?