Firefox chooses Mistral without locking its assistant into a single model

Mozilla adds Mistral Small 4 to Firefox Smart Window in France and North America, featuring interchangeable models and a promise of no conversation retention.

An assistant capable of summarizing a page, comparing several tabs, and retrieving a previously visited website may receive an especially revealing share of its user’s digital life. Mozilla wants to bring these features to Firefox without permanently entrusting that position to a single AI provider.

The organization is adding Mistral Small 4 to Smart Window, its new AI-assisted browsing environment. The French company’s model is becoming available in the United States, Canada, and France. France is the first market outside North America where the feature is being officially offered in French.

Mistral’s announcement states that Smart Window is now “powered” by its models. That wording may suggest that the company is becoming the assistant’s exclusive provider or that every AI feature in Firefox will now rely on its infrastructure. Neither is the case.

Mistral Small 4 joins a selection that also includes Google’s Gemini 3.1 Flash Lite and Alibaba’s Qwen3-235B. Users choose a model when they first use the feature, can change that selection in the settings, and can even use a different model for a particular conversation without altering their default preference.

The partnership also applies specifically to Smart Window, not to Firefox as a whole. It does not replace the user’s chosen search engine, the different assistants available through the browser sidebar, or the other experimental features grouped under Firefox’s AI controls.

Smart Window is presented as a browsing environment separate from the standard Firefox window. Its assistant can summarize the displayed page, answer questions about its content, compare information across multiple tabs, organize those tabs, and close duplicates. It can also help resume an interrupted search using certain elements from the browsing history.

The system does not, however, operate as an autonomous agent with control over the browser. Mozilla’s documentation states that it cannot click buttons on a website, fill out forms, complete purchases, make reservations, change Firefox settings, or sign in to an account. Its capabilities remain focused on researching, explaining, and organizing information.

When a question requires current information, Smart Window can also use Exa’s search engine. Exa retrieves webpages from the internet, then provides their content and references to the assistant. Research and response generation therefore rely on two separate providers: Exa retrieves current sources, while the selected model interprets them.

This separation allows Mozilla to replace one component without rebuilding the entire product. Mistral provides a language model but does not own the browser, the interface, or the system responsible for finding recent webpages. Firefox retains control over the layer that determines which information is shared and how the result is presented.

Mozilla says it selected Mistral Small 4 following internal evaluations covering page summaries, questions about page content, product comparisons, real browsing scenarios, and the handling of sensitive material. Its multilingual performance also factored into the decision to bring Smart Window to France.

Released by Mistral in March 2026, Small 4 is a mixture-of-experts model containing 119 billion total parameters, with 6 billion activated for each token. The input and output layers bring the active total to approximately 8 billion parameters. Its context window supports up to 256,000 tokens.

The model normally accepts both text and images and offers adjustable reasoning-effort levels. Mistral positions it for general conversations, document analysis, coding, and tool-based tasks. These capabilities do not mean that every feature is necessarily exposed through Smart Window, whose interface and permissions remain controlled by Mozilla.

The weights for Mistral Small 4 are published under the Apache 2.0 license. They can be downloaded, modified, and deployed on independent infrastructure. This is the primary basis for Mozilla and Mistral’s openness claims, particularly in contrast with models available only through remotely hosted services.

That openness does not turn the standard Firefox integration into a local deployment. When users select Mistral Small 4 from the built-in model list, their requests are processed on Mistral’s infrastructure. Gemini and Qwen, meanwhile, are hosted on Google Cloud.

The browser prepares a request that may contain the user’s question, relevant content from open tabs, stored memories, and any browsing information explicitly requested. The request passes through Mozilla’s servers before being forwarded to the selected provider.

This relay conceals the individual user’s IP address. Mistral receives a connection from Mozilla rather than directly from each Firefox installation. Mozilla and its partners also state that they do not retain conversation content or use it to train their models.

The privacy promise therefore depends on a combination of technical and contractual restrictions, not on the complete absence of data transmission. The full material required to produce an answer leaves the computer, passes through Mozilla’s infrastructure, and is processed by Mistral whenever its model is selected.

In this context, “private” should not be interpreted as meaning offline. It primarily means that the provider does not directly receive the user’s IP address, that conversations are not supposed to be retained, and that they must not be used to improve the models.

Conversations are stored locally so users can return to them later. They can be deleted from Firefox. Smart Window also includes a memory feature designed to preserve useful information, such as an interest or a previously expressed preference.

These memories are stored on the device and can be reviewed, deleted, or disabled. Their creation introduces an additional qualification, however. Smart Window’s privacy notice states that memories may be inferred temporarily on a Mozilla server before being returned to the