The Log Information Pages (LIP) for the write-ahead log are not currently used, though code to use them is included conditionally in Firebird.
This structure is no longer in use within the database, it is effectively, a wasted page. Discussions have taken place on the Firebird development mailing list on removing this page altogether as it is not used and the wasted space could be better used elsewhere. From Firebird 3.0 it is likely that there will not be a WAL page in any new databases.