This extension (formerly known as Yomichan) is used to easily look up words in your immersion by simply hovering over them with your mouse. It also integrates with Anki and makes sentence mining easy, as you can learn about in our sentence mining guide:
Yomitan – Get this Extension for 🦊 Firefox (en-US)
[ ] Set your scan settings. Here’s our recommendation:

[ ] Switch Language to Chinese:

[ ] Download Chinese dictionaries: (don’t unzip the actual dictionary folders)
We suggest:
For bilingual (Chinese→English) definitions:
CC-CEDICT.zip (for Pinyin) OR CC-CEDICT.Zhuyin.zip (for Zhuyin): ⚠️ Important: Make sure it’s the right CEDICT file - there are three, one for Pinyin, one for Zhuyin, and a special one for Hanzi. We recommend you choose only one - either the Pinyin one or the Zhuyin one.
For monolingual (Chinese-only) definitions (only if you are an intermediate or advanced learner, stage 2C or higher)
(Source 1, Source 2, Source 3 — also has other dictionaries you might find useful)
[ ] Optional: Download frequency lists to see how frequent words are in casual conversation and/or literature (you don’t need to unzip the individual frequency list zip files, just the container zip file, zhfreq_lists.zip)