It would be good if others could do this too. As I understand it, there is no real spec that explains how they should go about these situations, so it's all a matter of convincing them to do A or to do B.
Internet Explorer happens to do the thing that would make BookJs footnotes work automatically (no canvas editor solution needed, we would only need a work-around for Firefox), so the solution Chrome had implemented in which they copied Internet Explorer's behavior would have been really good for us. But apparently there is someone in the Chromium camp who is opposed to this, or questions it. At any rate, any solution will be better than the current behavior, especially if they copy the behavior of another browser.