Mozilla Adds Mistral Small 4 to Firefox’s AI Browsing Beta

Firefox’s Smart Window beta is gaining Mistral Small 4, giving users another AI model for help with searches, past browsing and open tabs. Mozilla and Mistral announced the partnership September 16; the model is coming to beta users in the United States and Canada, while France gets expanded beta access and official French-language support.

Mozilla selected Mistral Small 4 after evaluating its performance for Smart Window, including multilingual performance. The assistant is meant to help users follow complex search trails, recover something they previously viewed and present sources from their browsing.

More than a sidebar chatbot

Smart Window is optional and opt-in. Once enabled, it can process browsing activity to provide its AI features, including retrieving pages a user visited in classic or Smart Windows. Mozilla says it can also take requested actions such as closing or organizing open tabs.

Choice does not mean local processing

Firefox users can choose which AI model powers the assistant, switch models, or configure Smart Window with their own model endpoint. A custom endpoint outside the Smart Window interface receives information directly rather than through Mozilla, under that provider’s own terms and privacy notice.

Controls around browsing context

• Mozilla says Smart Window does not retain chat logs without permission and does not train models on Smart Window interactions.
• Memories inferred from browsing activity are stored locally after processing, and users can review, delete or disable them.
• Private Window activity is not used to create Memories.

Mistral has agreed to zero data retention for its role in the partnership, according to the companies’ announcement. Mozilla expects the partnership to reach the United Kingdom and Germany later in 2026. The rollout now tests whether multilingual tuning and model choice give users a reason to pick a model rather than simply accept a browser default.