Most likely since 2019: https://commits.webkit.org/211106@main The DocumentLoader re-enables the feature, unconditionally... m_frame->settings().setMediaSourceEnabled(m_mediaSourcePolicy == MediaSourcePolicy::Default ? Settings::platformDefaultMediaSourceEnabled() : m_mediaSourcePolicy == MediaSourcePolicy::Enable); in our ports Settings::platformDefaultMediaSourceEnabled() returns true and we don't use the MediaSourcePolicy API.