Validate Facebook accounts
Validation of Facebook accounts is very similar to validation of E-mail accounts
When validating, the software attempts to log in to Facebook account using the provided username and password. If attempt is successful, account is said to be validated, otherwise it is marked as invalid.
Validated accounts display in GREEN color, invalid - in RED color
If an account is neither green nor red (most probably, gray) then it has not been validated yet. The software will attempt to validate accounts automatically shortly after they have been created or imported.
You can also check this article for more information