You will have an option to use public AI's, or something you run locally via some software like Ollama for example. Which is quite awesome imho, because no other browser offers that. They all have some version of their chatGPT assistants and no other...
You don't have to used it. You also can use local LLM's for full privacy. If you download larch version of Firefox you can see it for yourself. It is completely configurable if you want to use it and what you want to use. Mozilla did a good job there...