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Certain Subdomains don't blur out

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On Firefox Developer Edition, the URL is displayed in full with protocol and subdomain greyed out, domain name shown clear, and URL path also greyed out, as is standard. Examples attached include developers.cloudflare.com and chat.openai.com

However, I've noticed on a few domains the subdomain is not greyed out and shown clearly like the apex domain. Examples attached include uwu.ai (a paid subdomain provided by carrd.co) and pages.dev (default subdomain for Cloudflare Pages).

What manages this behaviour? Why do some subdomains get treated as apex domains would on Firefox Dev?

On Firefox Developer Edition, the URL is displayed in full with protocol and subdomain greyed out, domain name shown clear, and URL path also greyed out, as is standard. Examples attached include developers.cloudflare.com and chat.openai.com However, I've noticed on a few domains the subdomain is not greyed out and shown clearly like the apex domain. Examples attached include uwu.ai (a paid subdomain provided by carrd.co) and pages.dev (default subdomain for Cloudflare Pages). What manages this behaviour? Why do some subdomains get treated as apex domains would on Firefox Dev?
Attached screenshots

Chosen solution

Those are effective top-level domains (eTLD) which can be found on the Public Suffix List (PSL).

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Chosen Solution

Those are effective top-level domains (eTLD) which can be found on the Public Suffix List (PSL).