Hmm, I designed the script so that in case of failure, it would fall back to the behaviour from before the change. That is, to rely on data fetched from the server every ten minutes separately in each tab that is currently visible.
This means that with the old script, tabs were already bound to be out of sync (and we occasionally had people comment that the counter never seemed to decrement, for example). Of course, there could be a bug that prevents it from working that way under special circumstances (I see that you are using an old version of Firefox).
I will make sure to look into it, but are you sure that there has been a change to the behaviour you used to see?