We appreciate your report. I was able to reproduce the issue. The page from the middle down is rendered incorrectly :

Tested with:

Browser / Version: Firefox Release 113.0.2 (64-bit)/ Firefox Nightly 116.0a1 (2023-06-05) (64-bit) Chrome Version 114.0.5735.110 (Official Build) (64-bit)
Operating System: Windows 10 PRO x64

Notes:

1. Reproducible regardless of the status of ETP.
2. Reproducible on the latest build of Firefox Nightly and Release.
3. Works as expected using Chrome:

Moving this to NeedsDiagnosis for further investigations.

[qa_23/2023]

They're using CSS :has(), which is not supported on Firefox yet:

.coreContainer:has(> #KSTL-landing-container-child-four-sub-child-two) #KSTL-landing-container-child-four-sub-child-two

But even with layout.css.has-selector.enabled enabled in about:config, the CSS doesn't seem to be applying. @dholbert, do you think this is related to the combination of CSS container queries and :has?

I should probably redirect your question to @emilio who's more familiar with the state of our :has and container queries implementations -- emilio, could you take a look?

(Or possibly @dshin-moz could take a look; he's working to get our :has impl to a state where we can turn it on. It's possible this is one of the known bugs in that feature.)

Ah, this looks to be a static case (i.e. it doesn't get invalidated through JS), which we should be able to render correctly 116 on (i.e. After bug 1793012 resolved).
I can in fact confirm that on Nightly 116 on that this works correctly with layout.css.has-selector.enabled set.

Thanks! Then let's close this as a duplicate of the main :has bug for Firefox, since there isn't much we can do here if Pringles insists on using these new CSS features before they're considered stable.