We should build webkitgtk4 with support for subtle crypto [1]. All we need to do is add a BuildRequires for gnutls-devel. Blocking FE-Legal out of caution. I'm not aware of any problems and I believe our Firefox package already implements the same features, but I've done no research. [1] https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto
After further discussion upstream, we decided to disable subtle crypto by default on all distros, since the feature is not fully complete.