Every major browser now has an AI sidebar, and Firefox is the last to show up. Smart Window, available in Firefox 149.0b7 beta, replaces the standard new-tab experience with a prompt box and pairs it with an AI panel that can answer questions about whatever page you're viewing.
The feature isn't turned on by default and requires toggling experimental flags. In testing on macOS, it worked as advertised. On Linux, it reportedly does nothing even with the flags enabled.
Three Models, No Default Lock-In
Smart Window offers a choice of three AI backends:
- Fast - Google's Gemini Flash Lite
- Flexible - Alibaba Cloud's Qwen3-235B (a 235-billion parameter model)
- Personal - OpenAI's GPT-OSS 120B
There's also an option to plug in a custom LLM via API endpoint, though local models reportedly have compatibility problems. The multi-model approach is a clear differentiator from Edge (locked to Copilot) and Chrome (locked to Gemini).
What It Can and Cannot Do
Smart Window handles web searches, summarizes page content, and answers follow-up questions. When you type a factual query, it runs a Google search and shows traditional results alongside an AI-generated summary in the sidebar.
What it will not do: interact with websites directly. No form-filling, no clicking buttons, no shopping on your behalf. That's a deliberate choice. Perplexity's Comet browser, which does let AI agents click around the web, has already run into legal trouble over that approach. Mozilla is playing it safe.
A Privacy Red Flag
Here's the problem. During testing, Smart Window's "memories" feature auto-populated with browsing history from months before the feature was ever activated. That data was then available to be shared with whichever third-party AI provider you selected. Mozilla acknowledged this is a flaw and said the onboarding flow needs work before a stable release.
For a browser that has built its reputation on privacy, shipping a beta that silently feeds old browsing data to external AI companies is a bad look. Even as a beta-only issue, it signals that the rush to add AI features is creating blind spots.
Early Verdict
Smart Window is functional but unfinished. The model selection is genuinely useful, and the non-agentic approach avoids the legal minefield other AI browsers are stepping into. But the privacy issue needs to be fully resolved before this ships to Firefox's general user base. If Mozilla can nail the consent flow and get Linux support working, this could be a solid middle ground between Chrome's Gemini-only approach and the more aggressive agentic browsers.