Browser Storage Abuser is a tool to experiment your browser storage limitation on LocalStorage, SessionStorage, WebSQL Database, IndexedDB API and FileSystem API. You can add arbitrary sized files to those storage to see the limit of their size.
On Chrome or Opera, you can also use the Quota Management API to inspect remaining size and to switch between Temporary Storage and Persistent Storage. On Persistent Storage, you can set upper limit of storage size.
See it running at http://demo.agektmr.com/storage/