The Web Extension is currently in development and only works on Firefox.
Download XPI file from the latest release of the Web Extension.
If you're using Firefox, a pop-up will appear to install it.
If you choose not to install the XPI from the download prompt, you can install it manually.
In Firefox, go to the Add-Ons Manager (about:addons)
Choose "Extensions" on the left menu
Click the Cog icon
Choose "Install Add-on From File..."
Choose the XPI you just downloaded.