What changed in Firefox Smart Window in September 2026?

On September 16, 2026, Mozilla and Mistral announced a partnership that adds Mistral Small 4 as a selectable model in Firefox Smart Window beta for users in the US and Canada, and expands Smart Window beta to France with French-language support; the UK and Germany are planned for later in 2026. Mistral agreed to zero data retention, and Smart Window conversations are not saved on Mozilla's servers by default. Smart Window itself launched in beta in August 2026 with Firefox 150 in the US and Canada and already let users pick Gemini 3.1 Flash Lite, OpenAI's gpt-oss-120b, Qwen3-235B-A22B or a local model, with web retrieval provided by Exa.

Which is better, Firefox Smart Window or Gemini in Chrome?

They solve different problems. Smart Window is a model-agnostic assistant focused on tab context, tab grouping, visual history previews and privacy; it does not click through websites for you. Gemini in Chrome is a Gemini-only side panel plus an agentic 'auto browse' mode that can research flights or hotels across sites, but auto browse is limited to Google AI Pro and Ultra subscribers in the US. Choose Firefox if you want model choice and no server-side history; choose Chrome if you want an agent that acts and you already pay Google.

Is Perplexity Comet still the best AI browser in 2026?

For most people, yes. Comet is free with usage limits, has a real browsing agent, and is the only major AI browser available on Mac, Windows, iOS and Android. Its weakness is trust: an agent operating inside your logged-in sessions is a large attack surface, and Comet's model choice is Perplexity's, not yours. Firefox Smart Window beats it on privacy and model selection; Gemini in Chrome beats it on integration with Google accounts and Workspace.

Are these AI browsers free?

Firefox Smart Window is free in beta, including the Mistral Small 4, Gemini 3.1 Flash Lite, gpt-oss-120b and Qwen options, and local models cost nothing beyond your hardware. Gemini in Chrome's side panel is free, but auto browse requires Google AI Pro or Ultra. Perplexity Comet is free with usage limits and unlocks higher limits with Perplexity's paid plans. ChatGPT Atlas, which some roundups still list, stopped working on August 9, 2026 and cannot be downloaded.

Quick Answer

Firefox Smart Window vs Gemini in Chrome vs Comet (2026)

Published: September 18, 2026

The short answer

Firefox Smart Window (now with Mistral Small 4, added September 16, 2026) is the privacy-first, model-agnostic option. Gemini in Chrome is the deepest Google integration with an agent gated behind AI Pro/Ultra in the US. Perplexity Comet is the free, cross-platform default with a real agent and the weakest privacy story. None is a clear winner; pick by whether you want choice, integration, or action.

	Firefox Smart Window	Gemini in Chrome	Perplexity Comet
Status (Sep 18, 2026)	Beta; US, Canada, France	Live	Live
Models	Mistral Small 4, Gemini 3.1 Flash Lite, gpt-oss-120b, Qwen3-235B-A22B, or local	Gemini only	Perplexity’s routing
Agent (clicks/types for you)	No	Yes — “auto browse,” AI Pro/Ultra, US only	Yes
Web retrieval	Exa, sources shown inline	Google Search	Perplexity search
Privacy	Chats not stored on Mozilla servers by default; Mistral zero retention	Google account data policies	Perplexity policies; agent uses your logged-in sessions
Platforms	Firefox desktop (150+)	Chrome desktop; mobile Chrome with Gemini	Mac, Windows, iOS, Android
Price	Free	Free side panel; auto browse needs AI Pro/Ultra	Free with limits; paid plans raise limits
Languages	English, French (Sep 16); UK, Germany planned 2026	Broad	Broad

Firefox Smart Window: choice and privacy

Smart Window grew out of Mozilla’s November 2025 “AI Window” concept and shipped in beta in August 2026 with Firefox 150 in the US and Canada. The August update added three capabilities: answer checks with inline sources (via a partnership with Exa, so you never leave for a results page), suggested tab groups with duplicate-tab cleanup, and visual history previews for finding a page you half-remember.

The September 16, 2026 Mistral partnership adds Mistral Small 4 as a model option for US and Canada and takes Smart Window to France with French support; the UK and Germany follow later in 2026. Mozilla says it chose Mistral after evaluating multilingual performance, and Mistral committed to zero data retention. Mozilla CEO Anthony Enzor-DeMeo framed the move as keeping the browser from becoming “a one-way funnel” to a single AI company; Mistral CEO Arthur Mensch called it “two open source advocates working together.”

The trade-off: Smart Window does not act. It summarizes, retrieves, organizes and remembers. If you want a browser to book the flight, this is not it. Also note that PCMag’s August review found answer quality depends on the model you pick; Fast mode on Gemini 3.1 Flash Lite is shallow, and Mistral Small 4 is a mid-size model, not a frontier one.

Gemini in Chrome: integration and a gated agent

Google put Gemini into Chrome as a side panel with awareness of your open tabs, and layered on auto browse, which Google’s own plan page describes as letting Gemini “complete tasks for you,” such as researching hotel and flight costs across multiple date options. The catch sits in the same sentence: auto browse is available to Google AI Pro and Ultra users in the US. The free side panel is useful for summaries and questions; the agent is a paid, US-only feature. There is no model choice — it is Gemini, on Google’s terms, under a Google account.

Perplexity Comet: the cross-platform default

Comet is free with usage limits, has a genuine agent rather than a summarizer, and Perplexity lists it for Mac, Windows, iOS and Android, which no rival matches. Its strength is research: reading across tabs, comparing sources, answering with citations. Its weakness is the one every agentic browser shares: it operates inside your logged-in sessions. Perplexity does not let you choose the underlying model the way Firefox does.

What is no longer on the table

ChatGPT Atlas stopped working on August 9, 2026 (292 days after launch); OpenAI moved browser-agent work into ChatGPT and Codex.
Arc has been frozen since May 2025; Dia (Apple Silicon only) is its actively developed successor under Atlassian.
Edge’s Copilot Mode as a standalone product and Perplexity’s acquired Sidekick are gone.

Decision guide

You want to choose (or self-host) the model and keep history off vendor servers → Firefox Smart Window with Mistral Small 4 or a local model.
You live in Google Workspace and will pay for AI Pro → Gemini in Chrome with auto browse.
You want a free agent on every device you own → Perplexity Comet, with a separate browser profile for anything logged-in and sensitive.
You want an agent but prefer the browser you already use → Claude in Chrome (paid Claude plans; its side panel has been a full Claude Cowork session since August 12, 2026).