window.crypto.getRandomValues. Code base has undergone two complete security audits from Cure53.
Noteable integration: Whiteout.io HTML5 mail App with integrated OpenPGP encryption from Munich, Germany. Usable as a chrome extension or self hosted (Node.js). They also offer free and paid managed mailboxed. The code has undergone a full security audit by Cure53. Users have the option to use encrypted private key sync if they want to use Whiteout on multiple devices.