Hi there! Run command to your Firefox (since v44~)

about:config

about:config => dom.push.enabled
dom.webnotifications.enabled => false
// and all messages, where you can see Push :)

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. 
Click the button promising to be careful.
(2) In the search box above the list, type or paste webno and pause while the list is filtered
(3) To disable PUSH NOTIFICATIONS, double-click the dom.webnotifications.serviceworker.enabled 
preference to switch its value from true to false -- sites can still generate desktop notifications while you have a tab open to the site
(4) To disable ALL NOTIFICATIONS, double-click the dom.webnotifications.enabled 
preference to switch its value from true to false -- this is a master switch, you won't get any desktop notifications from sites