If Mozilla wanna do it in the best way they should do a partnership with DeepL which is by FAR the best translating engine. It can understand the difference between a sentence on informal or formal dutch, can translate correctly a sentence using tuteo/voseo/ustedeo in spanish, and also can see not only the difference between British english and American english. In case of American english it can translate more efficiently some subtle words in sentences like "ain't" and "isn't".
DeepL makes every sentence sound human and not translated by a machine. Taking this approach can make some people move from Chrome to Firefox. Mostly spanish speakers were Google makes too much mistakes translating and sentences sometimes don't make any sense.