The Keybase browser extension adds Keybase Chat buttons to all profile pages, not just Reddit threads. We use the browsers Native Messaging API to speak with a small process which issued commands to Keybase (more details later) We use NativeMessaging to safely communicate with the Keybase service that is running on your computer. For now we only support Chrome, but other browser support will come once things settle down a bit. The extension is all open source under the BSD 3-clause license.”]
Source: https://medium.com/@shazow/working-on-the-keybase-browser-extension-ec3bed58a01