Google Chrome:
In order to add Betternet extension to your Chrome browser you need to open Chrome and browse this link to download the extension:
https://chrome.google.com/webstore/search/unlimited%20free%20vpn?hl=en-US
To use the extension please click on "Add To Chrome" Button.
Firefox:
For adding Betternet extension to your Firefox browser open your Firefox and browse this link:
https://addons.mozilla.org/en-US/firefox/addon/unlimited-free-vpn-betternet/
Now click on "Add to Firefox" button and install the extension on your browser.