The qz report suggests that users were more happy and less worried/sad if they stayed off Facebook, but it doesn't mention the (imo) more important part of the study.

The study says that most people "post their good sides on Facebook"

The study also says that many facebook users "envy" the amazing, happy and success related notes posted by their friends on facebook.

So it seems like you can stay happy on facebook and not feel worried if you

(a) understand that you should not envy your friends

or/and

(b) understand that you shouldn't take all facebook posts as face value and understand that you shouldn't assume that these posts represent your friends lives in entirety. You shouldn't assume that life is a bed of roses for your friends just because they posted the best parts of their life. It is likely that they have just as many problems and troubles as you do even thought their facebook posts may not capture all of these problems.