This is a very common problem with an easy fix. Apparently, it happens mostly on Chrome, but I have read that also happens (rarely) on Firefox and Opera too.
The main problem is that you can comment or Like a comment using the Facebook Social Plugin on any third party website, like 9GAG, because a message saying “Not Logged In – Please log in to continue” appears every time, even if you’re logged in.
Of course, many users claim that this happens because their Facebook was hacked or they have to change their password or anything related to your security, but most of the time is not related to that, is just that a third party cookie is being blocked by your browser. Let’s say I’m on 9GAG and I want to comment in the Facebook’s comment box; Facebook is the third party cookie, and it’s being blocked. Here’s how to fix it (on Chrome).
Ok, go to the site where you’re having the problem. In the address bar, click on the cookie that appears at the end, then on “Show cookies and other site data…”
This will popup a window showing which cookies were set and which were blocked. To fix the problem with the Facebook Social Plugin, you need to allow the www.facebook.com cookies to be set on the site you’re in.
After you do the changes you want click on Close. And reload the tab.
That should fix the problem.
It was clear to me..