Firefox 158 can suggest form entries from relevant open tabs as well as saved autofill data. Mozilla added the Smart Window feature in its October 13 release, with a gradual rollout rather than immediate availability for everyone. The useful change is the source of the suggestion: information already open elsewhere in the browser can become a candidate for the field you are filling.
That is a different proposition from asking a browser to remember an address. A saved address has a fairly obvious origin. A suggestion assembled with browsing context raises another question: which page supplied the information, and does it belong in this form? The convenience is less copying between tabs. The remaining work is deciding whether the proposed value is the right one.
Mozilla says users can invoke the feature by clicking a form field or selecting Fill from sources. The release notes do not present it as a guarantee that every field will be completed correctly. They also do not establish that a particular installation has received the feature simply because it runs version 158. The staged release matters when comparing two otherwise similar computers.
The data route matters more than the button
Smart Window is optional and requires a Mozilla account, according to its privacy notice. It is worth reading that notice separately from Firefox’s general privacy policy: Mozilla explicitly describes additional processing for the assistant. A familiar browser interface does not mean every operation stays on the device.
For the default assistant route, Mozilla describes sending the prompt, relevant browsing context and any relevant Memories to a Mozilla server, which forwards the request to a third-party language model. The provider sees Mozilla’s IP address rather than the user’s. That arrangement separates the provider connection from the user’s network address; it does not mean the request contains no browsing information.
Memories have a separate lifecycle. Mozilla describes these as inferred interests, stored locally after processing and available for review or deletion. It says the activity used to infer them can include classic Firefox windows, but excludes Private Windows. Turning back to a classic window therefore should not be confused with a universal statement about what previously enabled Smart Window features can process.
These details describe the assistant’s documented architecture, not a packet capture of Firefox 158’s form-fill operation. Mozilla’s release notes identify the form feature’s input sources, while the privacy notice explains the broader processing rules. Neither document supplies a field-by-field network trace. This article compares those documents rather than claiming a hands-on privacy test.
A suggested entry still needs a decision
A practical distinction is between finding information and authorizing its use. An assistant may locate a plausible value in another tab without knowing whether that value is appropriate for the receiving form. As an illustrative case, an address visible in a document could be a delivery destination or the sender’s office. Recognizing the text does not resolve that difference.
Mozilla’s Smart Window terms warn that assistant output can be inaccurate and call for users to assess it for their use case. Applied to forms, that means reviewing the actual proposed entry in context, rather than treating a populated field as evidence that the underlying information was verified. The same distinction between a generated action and its authorization appears in our earlier coverage of AI-agent permissions, although the products and controls differ.
Custom model endpoints add another boundary. Mozilla says a user-selected endpoint outside its offered interface receives information without routing it through a Mozilla server; a third party’s own terms and privacy notice then apply. The default route’s assurances cannot simply be transferred to that configuration.
For someone deciding whether to enable Smart Window, Firefox 158 makes the trade-off concrete: less manual transfer between pages, with browsing context entering the assistance process. The meaningful check is the source and destination of each suggested value. A faster form is useful only when it contains the information the user meant to send.