Try this Chrome Extension. It's called the productivity button. It allows you to hide/show the notifications with just one click of a button....it also allows you to set your chat status in normal and productivity modes:
I hated how Gmail shows G+ notifications, since I use Gmail for work and G+ for friends.
This program, at first I wasn't sure, but I am so happy that I installed it. Very quick and easy install (and then you need to restart FireFox once), and then Gmail is clean now.
Thank you very much!
I hate making accounts, but I did so that I can write this review for other people.