Unfortunately, Apple blocked user fonts in Safari: https://www.reddit.com/r/MacOS/comments/9jp5m3/psa_safari_12_disablednerfed_setting_custom_fonts/
I’ll write to author of the KanjiStrokeOrders font to ask whether he could host it on some CDN, or at least to ask for a permission to do it myself; not sure how it’ll turn out, but worth a try.