Modern IDB: fast/history/page-cache-indexed-opened-db.html needs a -private.html variant To support testing both in-memory and SQLite backends.
This test relies on sessionStorage, and sessionStorage is effectively disabled in private browsing. So the -private.html variant might be unworkable.
With this info, I don't think this should block the master Modern IDB bug. Instead once that bug is resolved, this one can be revisited. Changing the relation.