Firefox vs Vivaldi: Which Has Less AI?

Short Answer

Pick Vivaldi if you want a browser whose maker has pledged against an artificial intelligence (AI) chatbot, summary tool or suggestion engine, and you want a mail client, calendar and feed reader built in. Pick Firefox if you want an engine that is not Chromium, and an off switch that Mozilla says also covers AI features it has not shipped yet.

Neither browser wins on every point. Vivaldi is built on Chromium, and Firefox runs on Gecko, which Mozilla calls "the only independent browser engine left."

The pledge covers three features: a chatbot, a summarization solution and a suggestion engine. The blog post that makes the pledge is dated 28 August 2025 and signed by CEO Jon von Tetzchner. It adds a condition: "If AI contributes to that goal without stealing intellectual property, compromising privacy or the open web, we will use it." The pledge is a statement of policy, and the condition above applies to it.

Related comparisons: Vivaldi vs Brave sets Vivaldi's AI position next to Brave's, and Brave vs Firefox covers Firefox's AI switch in more steps.

Firefox vs Vivaldi at a Glance

The table sets the two browsers side by side on six points.

Vivaldi's AI Pledge and Firefox's AI Controls

Vivaldi has made a policy promise about one kind of AI, and Firefox has given you one switch for its own AI features.

What Vivaldi Has Promised

Vivaldi's CEO, Jon von Tetzchner, wrote the pledge on 28 August 2025 in a post titled "Vivaldi takes a stand: keep browsing human." It says "we will not use an LLM to add a chatbot, a summarization solution or a suggestion engine." That sentence names three features. It does not mention translation, which Vivaldi lists among its built-in features.

The same post sets a condition: AI can come in if it does not steal intellectual property, compromise privacy or harm the open web.

Vivaldi's 2025 review adds a user-research figure. Von Tetzchner wrote that when users were asked about AI in the browser, "The answer was ranging from 'no' to 'hell no' for 95% of the users." That is Vivaldi's own account.

How Firefox's AI Controls Work

Firefox 148, released on 24 February 2026, added an AI Controls section to Settings for managing AI-enhanced features, according to the Firefox 148 release notes.

1. Open Settings and choose AI Controls in the left column. Mozilla's AI Controls support page gives the same path.
2. Turn on "Block AI enhancements." It covers translations, PDF alt text, AI tab grouping, link previews and the sidebar chatbot.
3. Mozilla says the switch covers upcoming AI features as well as current ones, so a feature added in a later release falls under the same switch.
4. Each feature has three states: Available, Enabled and Blocked.
5. Blocking a feature also deletes any on-device model Firefox downloaded for it.

For a harder block of the chatbot, open about:config and set browser.ml.chat.enabled to false. That stops the chatbot loading. Hiding its button alone does not do that.

The sidebar chatbot is not a Mozilla model: it passes your prompt to a company you choose from Anthropic, OpenAI, Google, Microsoft or Mistral.

Firefox's translation is one of the AI features its switch blocks. Vivaldi's translation is a listed built-in with no stated technology, so whether it uses AI is unpublished.

What Each Engine Means for You

Vivaldi is built on Chromium, and Firefox runs on Gecko. Mozilla calls Gecko "the only independent browser engine left."

Vivaldi's own changes are made to the Chromium source code, and Vivaldi says all changes to that code are available under a BSD licence. Its user interface is written in HTML (the markup for page structure), CSS (styling) and JS (JavaScript, the scripting language), which Vivaldi describes as plain, accessible code.

Source availability is a separate question from the engine. Vivaldi's open source help page says Vivaldi "is not made available under one unified open source license." The interface is auditable, but the browser is not under one open-source licence.

If you need an engine that is not Chromium, Firefox meets that requirement and Vivaldi does not. If the Chromium base does not bother you, the engine is not a reason to choose Firefox.

Built-In Features on Each Side

Vivaldi ships a long list of built-in features, and Firefox's listed built-in controls are its AI switch and its tracking protection. The Vivaldi features page lists these items.

• A mail client, which the page calls a "unified inbox"
• A calendar
• A feed reader, which Vivaldi describes as "algorithm-free"
• Notes
• An Ad Blocker and a Tracker Blocker
• Tab Stacks and Workspaces
• Built-in translation

Firefox's Enhanced Tracking Protection blocks ad trackers by default, but it does not block the adverts themselves, so ad content needs a separate content blocker add-on. Vivaldi lists an Ad Blocker and a Tracker Blocker as built-in features. If you want ad content blocked without installing an add-on, Vivaldi's built-in Ad Blocker covers that.

Translation appears on both lists. Firefox's translation is covered by its AI switch. Vivaldi's translation is listed without a stated technology. Tab Stacks and Workspaces appear only on Vivaldi's list. Firefox's AI tab grouping is covered by its switch.

Where Each Browser Runs

Vivaldi's download page lists Windows, macOS 13 and later, Linux as Debian package (DEB) and Red Hat Package Manager (RPM) builds, Android through Google Play and as an APK (the Android app file format), iOS through the App Store, and Android Automotive.

Who Owns Each Browser and How It Earns

Vivaldi is employee-owned, with no external investors, and it lists partner deals and donations as income. Mozilla's audited 2023 statements report $494.9 million in royalties, and about 85% of its revenue from customers with contracts came from one customer.

Vivaldi Technologies was founded in 2013 by Jon Stephenson von Tetzchner and Tatsuki Tomita, with its headquarters in Oslo, Norway. The Wikipedia entry on Vivaldi Technologies describes it as "employee-owned, and derives revenue from product placement but not data." Vivaldi's own company page says Vivaldi is based in Norway and Iceland, has "no external investors," and reports "4.0 million users (and counting!)."

Vivaldi's company page lists four income sources: partner deals with search engines, partner deals with bookmark partners, partner deals through Direct Match, and donations.

Firefox's figures come from Mozilla's audited statements for 2023. The share of revenue from one customer was about 85% in 2023 and 81% in 2022.

Which One to Pick

Pick Vivaldi if the AI pledge and the built-in extras count for more to you than an engine outside Chromium. Pick Firefox if the engine counts for more.

Pick Vivaldi If

• You want a browser whose maker has published a policy against an AI chatbot, summary tool or suggestion engine.
• You want a mail client, calendar, feed reader and two blockers built in.
• You accept a Chromium base, and you accept that Vivaldi's interface is auditable but not under one open-source licence.

Pick Firefox If

• You want an engine that is not Chromium, and Mozilla calls Gecko "the only independent browser engine left."
• You want one switch that Mozilla says also covers upcoming AI features.
• You will install a content blocker for ads, because Firefox's built-in protection stops trackers and leaves the adverts in place.

Who Should Skip Each

Skip Vivaldi if you need an engine outside Chromium, because its changes are made to the Chromium source code. Skip Firefox if you want ads blocked as soon as you install it, because Enhanced Tracking Protection does not block the adverts themselves.

What Would Change This Answer

If Vivaldi's translation turns out to run on AI, the AI gap between the two browsers narrows, and Vivaldi has not said that it does. If Vivaldi changes its pledge, or uses AI under its own condition, the AI reason to choose Vivaldi weakens. If Mozilla's AI Controls stopped covering a feature Firefox ships, the reason to choose Firefox on AI weakens by the same measure.

If neither browser fits, see our browsers without AI guide and our Firefox vs Chrome page.

The two browsers each have a head-to-head with Brave: see Brave vs Firefox and Vivaldi vs Brave.