+1 from me on Keybase.io Chat extension (it has been suggested on GitHub).
This is the link of the extension:
Keybase for Chrome is an official Keybase extension for composing ENCRYPTED messages to any Twitter, Facebook, Reddit, HackerNews, or Github user, from the convenience of your browser. It’s an easier chat, and it’s end-to-end encrypted.
This works even if they have yet to join Keybase. The quick summary:
• Everyone with a social network account has a Keybase inbox, even before they join Keybase
• You don’t need to know the recipient’s email address or phone number or Keybase username—just a social media username is enough
• No one (at Keybase or the social networks) can read your private exchanges
• Look for the “Keybase Chat” button on profiles around the web
• Toggle specific features in the extension options (chrome://extensions/ and click on “options”)
At no point in Keybase’s protocol does Keybase ever have the keys necessary to read your messages. This is end-to-end encryption, powered by the convenience of public social media usernames.
By copying the extension to app folder and adding some modifications (changing the folder name etc), it actually works! (You’ll need to restart the browser to make it work)