Changes/fixes:
- Backed out the NSPR/NSS update from 27.8.0 for causing crashes, general operational instability and handshake issues.
- Disabled TLS 1.3 draft support by default, because with the NSS backout we only support an older draft right now that is no longer current and may cause connectivity issues. You can manually re-enable it at your own risk in about:config by setting security.tls.version.max to 4.