Works only on X/Twitter and it does so perfectly. If you're using the black theme, the furigana might not show, but you can customize the color of the furigana so you are able to see it. You can also increase the font size. Great extension for Japanese learners. Thanks!

你好 最近域名被改成X.com所以插件失效了 請問Firefox瀏覽器上的也可以幫忙做更新或是改版嗎

太牛逼了，谢谢谢谢