I finally found an add-on that is almost identical to the Chrome add-on TransOver (https://chrome.google.com/webstore/detail/transover/aggiiclaiamajehmlfpkjmlbadmkledi?hl=en).

I have a bit of greed about this add-on.
It would be nice to show the definition of a word like TransOver, rather than a Google translation.

Thank you for your efforts.

I've tried it and actually it works great!!
Besides, it needs some improvements, let's say:
+ Language of selected text: Japanese
+ Target language: English

Currently, when I select Japanese text, it translates text to English. It's OK in this case.
But when I select English text (that is same as Target Language), and my setting for second language is FRENCH, then I have to click on the icon button on the toolbar to see the translation to FRENCH, and cannot see directly on Translation Panel.

==> IMPROVEMENT: it is expected it AUTOMATICALLY translates to SECOND LANGUAGE and directly displays on Translation Panel in case Target Language is same as language of selected text.
Many thanks.

the simplest translate add-ons i've ever used

Very good! Simple, and useful! That's what I was searching for..
Thank you!

the best translator I've used on firefox (I tried all of them)

브라우저 내에서 간편하게 구글 번역 기능을 쓸 수 있게 해줍니다. 매우 유용합니다.

thanks

Funciona muito bem. Eh rapida e fluida.

크롬 기능과 가장 유사하게 사용할 수 있다. 편하다! 추천!

Perfetto

I miss a bunch of features:
1) customisable hotkey
2) pronunciation
3) grouping translation variants, not just showing a list of words

wonderful simple

work great