Works.. okay.

Starts disabled which makes it seem like its not working at first, only functions on "Write this in English" questions (doesn't work on wordblocks for instance), and there's a noticeable delay for loading the furigana on each question.

Otherwise it does what it intends to do and there's no better options, so hey.

ありがとう

it doesn't inline any romaji to any text on the page, and no shortcut either. click on icon nothing happens.

I was waiting for official support of the Furigana from Duolingo, but guess it'll take some time. I really like this extension. Pretty convenient. Thank you, Cieric