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When I try to close my Google docs tab with unsaved changes, this is what I get in my browser (FF 3.5).
Are you sure you want to navigate away from this page?
You have unsaved changes in this document. Click Cancel now, then 'Save' to save them. Click OK now to discard them.
Press OK to continue, or Cancel to stay on the current page.
My question is whether such alerts are part of the web app (gdocs for eg.) or are they given out by the browser? If latter, how is this done?