Comment 153 for bug 215728

urlclassifier2.sqlite is the old filename and is not used anymore.

The schema/filename policy reads like this:

// The database filename is updated when there is an incompatible
// schema change and we expect both implementations to continue
// accessing the same database (such as between stable versions of the
// platform).
#define DATABASE_FILENAME "urlclassifier3.sqlite"

// The implementation version is updated during development when we
// want to change schema, or to recover from updating bugs. When an
// implementation version change is detected, the database is scrapped
// and we start over.
#define IMPLEMENTATION_VERSION 4

This update only bumped IMPLEMENTATION_VERSION.