Among the 'Dictionary Anywhere' forks, 'Lexikon' is, in my opinion, the most accomplished, with real improvements such as the personal dictionary and the dark theme. There's no doubt that it will continue to evolve to include even more features.

This add-on is amazing, I find myself using it multiples times everyday.

It's quick to activate it (double click a word), the response is instantaneous and very efficient. The pop-up bubble has a "More>" button if the provided definitions aren't enough. I never had to use it.

Finally, the developer is a very kind person and is willing to discuss any enhancements, bugs or feature requests, if they're feasible.

Amazing extension, its much better than the other one. I like the personal dictionary and multiple definitions. The language switcher is great for bilinguals.
I just miss one things synonyms and antonyms. If it could get that it will be awesome