Updated March 14, 2019: Facebook and the other sites managed by Facebook should be up again. My Facebook and related sites came back up about 10 P. M. U. S. Central Time although many had access earlier.
I am posting this on the off-chance somebody isn’t aware of it. It doesn’t matter if you use Facebook rarely, but you use it to log-in on other sites. I have a few sites that I never set up a separate log-in as Facebook is rarely down. I will be re-thinking my decision as some sites have other options for logging in. If you are trying to log-in on a site where you only have Facebook access, you won’t be able to sign-in until it resolves the problem.