@bert_hubert I ended up turning that off again after trying it since it got introduced, since it kept popping up when I didn't need it, and, AFAICT, only works on a site level, instead of, say, selected text?
I may have missed something, but it felt very unintuitive.
@sindarina I can only say that this has not been my experience. But I have indeed not seen an option to only translate part of the text. According to https://support.mozilla.org/en-US/kb/website-translation that is not there.