localStorage is the same as sessionStorage with the same same-origin rules applied but it is persistent. localStorage was introduced in Firefox 3.5.

API Offline Reference Référence Storage API

A StorageEvent is sent to a window when a storage area changes.

API Reference Référence Web Storage API

Storage objects are simple key-value stores, similar to objects, but they stay intact through page loads.  The keys and the values are always strings (note that integer keys will be automatically converted to strings, just like what object do). You can access these values like an object, or with the getItem() and setItem() methods.  These three lines all set the colorSetting entry in the same way:

API Guide localStorage sessionStorage Storage storage Web Storage API