Safari Facebook Login

Hello,

I have a "problem" with Safari when trying to log-in to Facebook. After I insert my credentials and hitting enter, a small window (attached) pops up. When I choose "Leave Page", it brings me to my News Feed. But when I click "Stay on Page", it just stays on the facebook main page however I am unable to log-in after a short period (~20sec). This happened recently and was wondering how to stop it. Usually, it never gave me the option; I just had to put in my credentials then login. Also, in the midst of typing down my credentials, the window shows again if I try to exit the tab. Just to note, it appears to only happen with Safari and Facebook as I tried it on Firefox and Chrome along with other websites and no window ever shows, just smooth login.

Machine: Macbook Pro (13-inch, 2017, Two Thunderbolt 3 Ports)

macOS: High Sierra Version 10.13.4

Safari: Version 11.1

Thank you.