Huahua: Chinese Popup Dict от empanadadebondiola

This add-on allows you to look up chinese characters just by hovering over them on the browser.
Supports pinyin and zhuyin, with tone coloring, traditional and simplified characters.
Contains a built-in word list, where you can save and export any word you look up with the popup.

This is a fork of cschiller's Zhongwen popup with a few tweaks, for example picking words from popups to save only the ones you want.

Source on Github