Most of the notifications are not necessary. It just gives you bad habits and distract you. The addiction you describe is partly created by getting used of all these small notifications sounds that excite you and give you the habit of checking all your accounts in a terrific infinite loop.
When you think about it, it is not human, you have far more things to do than being distract by these little sounds. Most of the applications makes possible to set precisely when you want to be notified or not. Don't worry, even with notifications, you will still be distracted by your kids, cat, neighbors, flying birds and dust.
I don't think the browser extensions are a solution to this. You have to learn to control it by yourself.