Sorry to hear about this problem. I think the Notes extension was discontinued, so my first question is, is it still installed and enabled? Assuming so, does it show older data (as though it was rolled back) or nothing (like it was removed and freshly installed)? Did Firefox give you any unusual messages during the startup after the update? For example, saying that it needed to create a new profile or that some data would not be available? Did you notice any other changes or lost data?