4 month ago and still not working - it doesnt translate anything and says error in translate engine. If Mozilla propose users to use this addon then it should work at least.
I dont see why specific cpu demand is necessary for this very small addon! It should work with all cpus.
So I will remove it from my FF.
Also bad that on almost all mozilla pages other translators do not work!

Excellent interface et une très bonne traduction

Lacks a button to alter settings. I turned off the intrusive bar for translation suggestions, now I can't turn it back on. Can't find the settings to select, which languages I want to translate.

Also, it's missing an icon for quick translation of highlighted text.

5*, Außer dem Vorteil, dass meine Übersetzung nicht public wird, kann ich eine Übersetzung, ohne Tab-Wechsel zu google- oder yandex- -translate, durchführen. Ich habe bisher nur wenige Tests durchgeführt, will aber schon jetzt die App nicht mehr missen.

il est presque bien pour aider

J'aime bien FIREFOX !

Liefert schnelle Übersetzungen im Seitenlayout, Formulierungen grammatikalisch oft falsch, Satztrennung mangelhaft.
Sicher sinnvoll, wenn man nur einen generellen Überblick haben will, worum es geht.

pas encore expert

Enfin !!! Quel bonheur, vous savez toujour lier entre efficacité et facilité d'usage !
J'ai plus besoin d'aller sur Chrome... Quel bonheur :D

marche moins bien que simple translate, le texte traduit s'affiche avec une couleur transparante peu lisible, et ne traduit pas automatiquement le texte selectionné

parfaitement efficace

It's a cool thing that Firefox added its own translator as add-on. I hope it improves a lot and can become a competitor with Google Translate and Yandex Translate in the future.
Anyway, I tested it a bit on and I must say that for now it still needs to improve translations in some websites.

E.g.

- I tested it on Bandcamp and translated from English to Italian. Below the profile of an artist, there was written "Records" and Firefox Translations translated it to "i record", which isn't correct because there was the name of a label before.
(But at least this error was highlighted with red because I enabled the "Highlight potential errors in red" function, which is very cool in my opinion).

- I tested it on the Firefox Translations repo on Github and translated again from English to Italian. The "About" word of the About section on the top right of the rectangle with files got translated with "A proposito di"... Only a single word like "Dettagli" (details) or "Descrizione" (description) would have been correct.
Still, in the About section, "a webextension" got translated to "una web estensione", while at the beginning of the README.md the result of the translation was "un WebExtension"; both aren't grammatically correct. "un'estensione web" would be correct in Italian.

These are just a few examples to give the idea of what the translation errors can be and I hope this add-on will get better and better.