I think it's two-fold: rise of tools like curl-impersonate (https://github.com/lwthiker/curl-impersonate) and the very consistent Firefox TLS fingerprint across platforms. Unlike Chromium (where you could differentiate a Linux, Mac or Windows computer from its chiphers, and so for example challenge only Linux clients), Firefox has NSS and NSS is used everywhere the Gecko engine is used while Chromium, although has BoringSSL for modern chiphers, also uses the underlying TLS stack of the operating system (whether it's Microsoft's SChannel, Apple's SecureTransport or Linux's... NSS). The only time Chromium uses a pure BoringSSL implementation is on Android (Conscrypt).