Need some help with - FB page from stranger pops up

Hello everyone,

I hope I find someone who can give me a tip on a strange issue I have.

I am using Safari browser and when I want to log into Facebook, somehow a FB page from someone else is popping up, asking to verify his/her account with an ID. I cannot even sign out of , it just keeps coming back, and I cannot sign in into my own FB, only when I use another browser.

Anyone's got an idea how I can get out of this mess?