Ctrl+w? I'm pretty sure there are mass bookmark extensions. Get one of those and dump all open tabs into a triage folder; once a week go through the folder and

Ctrl+w? I'm pretty sure there are mass bookmark extensions. Get one of those and dump all open tabs into a triage folder; once a week go through the folder and move the ones you want to keep into a proper folder and delete the rest. Hell, that ought to be an extension too. Autopurge a bookmark folder at set intervals.