It’s good question. If a Mozilla people interesting for it - feel free to email me. As i know, for now a firefox translator is just a wrapper over Bergamot Translator while time a Linguist is a common purpose translation system for all major browsers, that embedded a Bergamot Translator as one of a great translator implementations.
For now Linguist had no reviews by influencers and it did not appears on reviews of a firefox addons blog unlike some other addons like proprietary Mate translate and open source TWP - Translate Web Pages. If we together make Linguist visible for a wide people, maybe Mozilla will pay attention for a Linguist too and we can integrate Linguist into a Firefox with all features it have