I've been using Session Buddy (www.sessionbuddy.com) for a few months now. It (optionally) automatically indexes your open tabs during a browsing session under

I've been using Session Buddy (www.sessionbuddy.com) for a few months now. It (optionally) automatically indexes your open tabs during a browsing session under their respective windows. You can go back later and label or augment these sessions with further browsing. This isn't exactly what you're asking for obviously, but you may find it useful anyways.