Rated 5 out of 5 stars

Exactly what I was looking for: simple, efficient, no frills. DeepL is a very good translation site. Thank you very much.
As improvements, I would see the opening of the translation in a pop-up window instead of a new tab, the reverse translation, the ability to copy the translated text and a keyboard shortcut.

This review is for a previous version of the add-on (1.0.0). 

Thanks for the review. Your requests have not all been fulfilled yet, but the popup window feature has been implemented in 1.1.0, so please try it out.