its called Invite post likers to like page in Facebook and it is for the Chrome browser (which you should have it you run FB ads)
All you do is;
1. open a Page Post,
2. then click the INV plugin button in the top-right corner of your browser,
and then plugin will automatically begin inviting people who "liked" your post to LIKE your page.
Basically it saves a lot of time and is a easy and free way to increase page likes.
More Page likes = more social proof and obviously cheaper ads to those page fans.
You can install it for free here https://chrome.google.com/webstore/d...ojodb?hl=en-US
I hope this helps!