That’s odd, are you using other extensions that add options to menus that do work? What version of the extension are you using?
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On further inspection none of my extensions are working, please disregard what I said before. I probably just imported them wrong. With this one and a couple of the others it also said “Error parsing JSON file: unexpected end of input” which lead to me opening the .aseprite-extension files with winrar and manually installing them.