When installing the PlayOn extension for the Firefox browser, Firefox will open a new tab titled Install Add-on when you open the browser. In this tab, check the box labeled Allow this installation and then click the Continue button. You will then be prompted to restart Firefox. You can click the Restart Firefox button.
The PlayOn extension will now appear as a small PlayOn logo to the right of Firefox’s search bar.
If you accidentally close this tab, you can enable the PlayOn extension through Firefox’s add-ons manager.