Ok I tried with another FB account and works fine, the loop was because I have the same email for my WP and FB account.
same think here. When I am already logged in to FB and open new tab to log in with my WP account into my site even if I didn’t click on the fb login , I get redirected to register form prifilled with my FB credentials. I ‘m agree with selfantagonist that not everyone want to connect fb with any site account.
