How is browser idle time determined?

[hassen1]

In the current implementation (Mozilla 1.2), idle time is determined using the nsIWebProgressListener API. We attach a listener to the toplevel nsIWebProgress object ("@mozilla.org/docloaderservice;1"). From this, we receive document start & stop notifications, and we approximate idle time as the period between the last document stop and the next document start. The last document stop notification occurs roughly when the onLoad handler would fire for the toplevel document. This is when we kick off prefetch requests. If a subframe contains prefetching hints, prefetching will not begin until the top-most frame and all its "child" frames finish loading.