Why not just have a timestamp in the query string? This way, each tab could have a different such timestamp of when the page was first loaded in that tab. When

Why not just have a timestamp in the query string? This way, each tab could have a different such timestamp of when the page was first loaded in that tab. When the page is refreshed, a new request will be made with the old (previously requested) timestamp. This requires, of course, that you are storing previously used timestamps somewhere, such as in the cookie; this also requires (somewhat) that the buttons on the app are asynch and don't change the timestamp.