"The webpage you are viewing is trying to close the tab"

Whenever I visit my website aggressive-interior.com a message pops up that says “The webpage you are viewing is trying to close the tab. Do you wish to close this tab?” With the choice of Yes or No. If I press No, the message reappears. If I press yes, the tab closes. It will not allow me to press anywhere else on the website. It started after I tried to download a facebook login plugin. I cannot click on my dashboard or plugins to deactivate it.

Please help.