The idea of Offline Applications is to make your favorite online services, such as web mail, available even when you are offline. Naturally in this situation you will not be able to send mail, but you should be able to read your old messages, and compose new messages that will be sent when you come back online.
of which the first two pertain to data storage, and the last to the resources that make up the layout and functionality of the website. A website that applies these specifications will make its resources available to you when you are online, and they will be saved to your computer.
Notice that the browser infrastructure required for offline applications is useful not just when you are offline, but also when you are online, because it lessens the need for contact with the server. Offline applications speed up online browsing, in much the same way as cache does.
Webpages using persistent storage
You can manage the list of websites that store information on your computer, according to the above specifications. Select a website and press "Delete" to delete the data and resources connected with that site. Click "Clear All" to delete the resources connected with all sites.
Use application cache
The default setting is "Yes", and since application cache is useful both when you are online and when you are offline, you may want to leave it. Choose "No" to disable caching of website resources, and "Ask me" if you want each individual website to ask for your permission.