Firefox 73.0.1 (64 bity). Dodatek nie działa, po wciśnięciu "T" nie rozpoznaje języka i czasem zawiesza przeglądarkę. Nie działa również tłumaczenie zaznaczonego tekstu.

Works perfectly. As expected.

Je l'ai déja utilisé et je l'ai trové pratique

Y

I think I had this addon since a long time ago, I have been using Nightly for at least 2 years and there it wasn’t working. But now, I just opened the standard Firefox and found it again. I remember selecting a text, right clicking and selecting in the context menu “Translate selection with Google Translate”. It then used to change the selected text with the translated text within the same page.
It now opens a new google translate tab, and there is no setting to change this. I would like it as it was before @nobzol, is there a chance to see this happening, please?
Yeah, the T on the bar does nothing, but I’ve never ever used it, so I personally don’t care. ☺

With Firefox 72.0.1 x64 in windows add-on does not work.

Like the author said on his page, they've downgraded with the WebExtensions incompatibility.