Sarah Jamie Lewis Hard-Forks Firefox to Delete Mozilla's AI Code

Sarah Jamie Lewis, executive director of the Open Privacy Research Society, spent the summer stripping AI-integration code out of Firefox, and on Sept. 19 she published an account of how much code that turned out to be: 1,605 files and 852,297 deletions in the first patch alone, built against Firefox 153 ESR.

The project, called Base Browser, started in July 2026 after Lewis called on a Mastodon thread for maintainers of existing Firefox forks to share a single, AI-free base rather than each stripping the same code independently. She describes herself as an unlikely lead on the effort: "I am not the right person to do something like this," she wrote, before doing it anyway. Work now happens in a Codeberg organization she set up to coordinate contributors.

What the 37-megabyte patch actually removed

Lewis's post describes the goal as complete removal rather than disabling: Firefox's AI features, in her account, have become "too large" and "increasingly tightly integrated into the core browser" to simply switch off. The initial patch weighed in at 37 megabytes. Over the following weeks, Lewis and a small group of volunteers compressed it to under a megabyte, using git's irreversible-delete flag alongside custom Python scripts to strip the deleted code's history rather than just marking it removed.

What Firefox's AI features do, according to Mozilla

Lewis's post does not name the specific features by title, so the target is easier to see from Mozilla's own side. Mozilla began rolling out Smart Window, an optional window where a user can chat with an AI assistant while browsing, to English-language users in the United States and Canada on Aug. 18. Ajit Varma, Mozilla's head of Firefox, described the feature by saying "the browser already has much of the context around what you're trying to do," citing open tabs and browsing history. Firefox's sidebar separately lets a user pick a chatbot, Anthropic Claude, ChatGPT, Google Gemini or Le Chat Mistral, to talk to alongside their browsing. On Sept. 2, Mozilla added an AI Controls section to Settings that can, in the company's words, "block current and future AI features and related pop-ups with the swipe of a toggle." Two weeks later, on Sept. 16, Mozilla expanded Smart Window into France with a French-language beta powered in part by Mistral's models.

Why deleting beat disabling, for Lewis

Mozilla's own toggle is the disable path Lewis argues is no longer sufficient. Her broader post reads Mozilla's direction over roughly the past decade as building toward a browser where, as she puts it, "the entire browser context is a 'smartwindow' built as much for a third-party AI agent" as for a human user, making a settings toggle a control Mozilla could add features around rather than a wall the code can't cross. Whether that reading holds depends on whether Mozilla keeps the toggle load-bearing as it adds more AI surface area, something only future Firefox releases can settle. Mozilla, for its part, describes the same features in terms of user choice rather than default direction: its Sept. 2 post frames AI Controls as letting someone pick between four separate levels of engagement, from a full opt-out to selecting individual features like translation or tab suggestions to choosing a specific chatbot, and says plainly that "the choice between them is entirely yours."

What Base Browser doesn't have yet

The Sept. 19 post is a status update, not a download page: it links to the Codeberg organization but not to a build, and Lewis's writing gives no version number or release date for a browser end users could install. Existing Firefox forks, including LibreWolf and IceCat, already ship their own AI-stripped builds today, and part of Lewis's goal is getting those projects to consolidate around one shared base rather than compete. Whether any of them adopt Base Browser's patch set, rather than continuing to maintain their own, is the detail that will decide if this becomes a shared foundation or one more fork among several.

Lewis's alternative to a chatbot sidebar

The deletion is only half of Lewis's Sept. 19 post; the other half argues for what a browser should add instead of an AI sidebar. She points to two long-defunct browsers, W3C's Amaya and the social-network-focused Flock, as examples of browsers built as creation tools rather than pure consumption tools, and describes her own experiments serving pages over the Gemini protocol and RSS as a way of testing what a non-AI "new noise" in browsing might look like. None of that is packaged into Base Browser yet; it reads as the argument Lewis wants the project to eventually serve, not a feature list already in the patch.

Date	Milestone
Aug. 18, 2026	Firefox Smart Window opens as an opt-in beta in the U.S. and Canada
Sept. 2, 2026	Mozilla adds an AI Controls toggle to Firefox Settings
Sept. 16, 2026	Smart Window expands to France with Mistral models added
Sept. 19, 2026	Lewis publishes the Base Browser patch's file and deletion counts

Source: Mozilla blog and sarahjamielewis.com, accessed Sept. 21, 2026.

The pattern of a maintainer rejecting a vendor's AI additions outright, rather than configuring around them, echoes a dispute earlier this month when a Void Linux package maintainer orphaned 113 packages rather than comply with a request to rewrite AI-flagged text. Browser vendors are also moving faster in general: Google cut Chrome's release cycle to two weeks starting Sept. 8, which, if Firefox eventually follows, would shrink Base Browser's window for rebasing each patch against a moving target even further.