This seems to be caused by different XBL bindings including the same stylesheets. Updating either of the stylesheets *seems* to affect all the users, though I don't understand how that can be the case. Ideally, we should hide the duplicates for the user if and only if it's a chrome page they're looking at (websites could theoretically send different content for the same URL requested twice). We should then ensure that updates work seamlessly for all users of the stylesheet.
Inspector bug triage (filter on CLIMBING SHOES).