While DbVisualizer does not provide a way to fully show the differences between two schemas in terms of objects and data, you can compare different aspects of a schema to another schema one by one. 

For instance, to compare the list of tables in one schema with the list of tables in another schema:

1. Expand the schema node for the first schema and select its Tables node and open it in a new Object View tab, select the Tables tab,
2. Do the same for the second schema,
3. Select "Compare..." from the right-click menu in one of the Tables grids to compare their grid content, or select Tools->Compare.

You can do the same for all the other schema object types, such as views and stored procedures. You can also dig deeper and compare the individual objects, such as comparing individual tables.