@Desemin Firefox Release (currently 128) we only have Russian to English. In Firefox Nightly we also have English to Russian.We are currently training higher quality Russian models. Once they are ready, we will deploy them to both Firefox Release and...
@gridsleep it works for local files too, but only if you keep the tab open and restore tabs when Firefox restarts.
Anyway, it's only a workaround, we agree the situation is not ideal and we will work on improving it.