Iv been checking out the web notifications (push notifications) that you can switch on for a lot of sites like twitter, youtube and reddit etc but they hardly ever work. On firefox this tester works while the page is open but not when the tab closed http://www.bennish.net/web-notifications.html but iv set reddit and twitter and a few other sites to allow notifications but i never see them.

This tester work great , even works when the tab is closed. https://serviceworke.rs/push-rich_demo.html

actually twitter does show the popup notifications but only while im actually on the site, other sites iv never seen notifications at all.

I have also noticed that if im using another browser for a while (receiving no notifications) and then open vivaldi or chrome i get an instant flood of notifications of all the things that should have notified me whilst i was using another browser but after that i dont get any more notifications at all from anything except from twitter but only while im on the twitter page

On reddit i used the preferences/messaging options/send message notifications in my browser/test button and it works fine but i never get notifications from reddit when i should be getting normal notifications. http://i.imgur.com/99rQ4L4.png

Iv tried it with firefox, Chrome, Vivaldi, Brave & Opera

EDIT:-
Im on Mint18.1 KDE plasma 5

Part of the issue could be that Mint 17.x was KDE Plasma 4.x all the way until 18 was released. Things probably aren't integrated or tested as well, and a fresh start with Mint 18.2 KDE's Plasma 5 could help

o sorry how did i get that wrong , im on mint 18.1 plasma 5.8.5

bump...

Now twitter does not do email notifications for individual tweets just a digest of things several days later so because i never got to figure the push notifications i dont get any notification of people trying to tweet at me at all.

Iv also installed ubuntu on another machine and it is exactly the same, web push notifications just dont work properly, sometimes i get them but mostly i dont and thats on all browsers on mint cinnamon & KDE & ubuntu.