Yomitan

Yomitan is a free pop-up dictionary extension for Chrome, Firefox, and Edge. It’s for learners who want to read real websites and look up words without leaving the page, especially if you like “vocab mining” into Anki.

You hover over text and press a key to open a definition popup, with options like pronunciation audio, frequency info, and a built-in search page. Setup centers on importing dictionaries, and you can manage different profiles if you study multiple languages. The official docs start here on the Getting Started guide.

If you use Anki, Yomitan can send your lookups straight into your deck using the AnkiConnect add-on, which makes it easy to turn reading into daily review. The extension listings also emphasize offline use once your dictionaries are installed, and privacy-minded defaults, as described on the Chrome Web Store page and Firefox Add-ons page.

Where it falls short for Vietnamese learners is dictionary availability. The recommended dictionaries list focuses on Japanese, Korean, Mandarin, and Cantonese, plus a few multilingual sources, so you may need to hunt down a good Vietnamese dictionary in Yomitan format before it becomes truly useful.