In the Gmail website settings, you need to click the '''Click here to enable desktop notifications for Gmail''' link in the '''Desktop notifications''' section to enable Gmail to send notifications to Firefox. That will open a popup to allow notifications from the website. You can check if notifications are enabled for Gmail by viewing the Firefox settings page and going to the '''Privacy & Security''' page. When you scroll down to '''Permissions''', you will see a '''Settings''' button next to the '''Notifications''' option. If you've correctly enabled notifications from Gmail, you should see Gmail on the list of allowed websites. If Gmail is already listed as allowed, click on the website and press the '''Remove website''' button. Then restart Firefox and enable notifications for Gmail again. See [[Web Push notifications in Firefox]] for more information.