Doesn't work on TaoBao, deepl, and some other sites I tried. Maybe something is wrong with my Firefox.

This is the only extension that's properly showing the pinyins in ruby text. I can't recommend enough. However, I would like to have an option to show the pronunciation in Zhuyinfuhao.

It does what it promises to do. I only know ~20 hanzi and they were correct so I assume the rest is also correct.
It's using a offline json dictionary file and does not send the data to a remote service (as far as I can tell) which is also a big plus.
It's only one button and the annotated text does not break the design of the site.
The only negative so far. You can't select the annotated text, which is fine for me.
Overall I'm very happy with this add-on.