I don't think that's necessary. If there's already a launch.html?url tab open when `open` runs, we should connect to that tab instead of opening a new one. I don't think poses a problem because the whole point of the interstitial page is to be able to mark a time that certainly precedes the page load of the target URL. If we find an old interstitial page with the same query string and with the load variable set to true, then that is also sufficient to mark a time previous to page load of the target URL.

Of course, if a completely different file is loaded at that URL, then we'll have a problem. While that's possible for the user to accomplish, that seems pathological and not worth defending against.