By default, DbVisualizer queries the ALL_OBJECTS system view in Oracle when populating the database objects tree. This view includes objects that you have created and objects to which you have privileges. 

If you have DBA privileges you may set up DbVisualizer to use the DBA_OBJECTS view instead. This view includes all objects in the database.

To change this in DbVisualizer, change the System Views Prefix setting to DBA_ for your connection. This setting can be found on the Properties tab in the connection view under Oracle -> Objects Tree.