Here is how to turn them off:
1. Click the "lock" icon to the left of the address bar on a Facebook page. Find "Notifications" and block them all.
2. Notifications can be also turned off globally via Chrome Settings:
https://www.facebook.com/help/community/question/?id=10153141912864103 (see top answers), but I guess you'd need to do p.1. anyway, because Facebook somehow got an exception (at least in my Chrome).