This works really great for what has already been added in... however, I'm unable to view the sample profile or add in new profiles (I can add or change entries in the existing profiles, but not import new ones - when I try to import, I get an error). I also can't seem to export a profile. Other than that being fixed, the only other option I think could really improve this add-on is if you added a "show original word upon hover", or "show note on hover" option. That way, when you hover over a kanji you can't remember, it will either show you the original word it had changed it from, or show you a note that you put in for the kanji.
This add-on could be fantastic for learning other languages as well, provided importing/exporting is fixed. Say you are learning German and replace "girl" in English with the German word, if you hover over the German word you could potentially see both the original English word and the gender for the word "girl" (which you put in as a note) for example.
I would give it five stars if these problems didn't exist!