Firefox's AI assistant now runs on Mistral, and Mozilla left the model picker in place.
Two companies that call themselves open source advocates are selling a browser deal as a brake on closed-model AI.
Mozilla and Mistral announced a partnership on September 16, 2026. The part you can use today sits inside Firefox: Mistral Small 4 goes into Smart Window, the beta AI browsing assistant Mozilla has run in the US and Canada since August 18, 2026.
France gets it the same day, in French. That's the first market Mozilla has added since the beta opened, and both companies wrote the deal up as an argument about who gets to be the model behind a browser.
- Model
- Mistral Small 4, new for Smart Window users in the US and Canada
- New market
- France, the first new market with official French-language support
- Expected next
- the United Kingdom and Germany, later this year
- Conversations
- aren't saved on Mozilla's servers by default
- Other models
- Firefox users can still choose from a multitude of other AI models
Why Mozilla picked Mistral
Mozilla says it picked Mistral Small 4 after testing it for Smart Window, multilingual performance included, and that the tuning went into regional languages and dialects rather than an English-first product pushed at a new market. The model picker surviving is the part I didn't expect. Mozilla names a partner model and, in the next sentence, says Firefox users "can still choose from a multitude of other AI models".
A browser shouldn't be a one-way funnel. It should preserve what made the internet powerful to begin with: the freedom to explore, discover different ideas and tech, and decide for ourselves where to go next
Arthur Mensch, Mistral's co-founder and CEO, gets reach out of it. Mistral's post says the company traditionally focuses on serving the enterprise (its usual customer signs a contract, and a Firefox user just downloads a browser), and that this deal extends it beyond businesses to consumers.
What the assistant does
Smart Window answers a question with its sources shown, so you don't start from a results page. It'll also group related tabs, flag duplicates, and show visual previews of pages in your history, which is how you get back the one you clicked away from an hour ago. I suspect that last one gets more use than the answering does.
On data, Mozilla says conversations aren't saved on its servers by default, and that partners like Mistral agree to zero data retention. That's a contract term. Neither post says who checks it.
- Smart Window beta opens, US and Canada
- Mistral Small 4 arrives, France added
What the two posts don't line up on
Mozilla's post names Mistral Small 4 for Smart Window users in the US and Canada; Mistral's says its models will help power the assistant in France and North America, without naming one of them. Neither prints a price, and neither says whether Mistral answers unless you go and pick it.
Mozilla says more of Europe comes later this year. The two markets Mistral names are the United Kingdom and Germany.