SigmaOS vs Firefox

We make Yab, the third column.facts checked Oct 9 ↓

SigmaOS is a Mac browser on WebKit that treats tabs like a to-do list, in workspaces down the side, with an AI assistant called Airis.

Firefox is Mozilla’s open-source browser on its own engine, Gecko, on every desktop and phone. Its AI is optional: a Smart Window beta and a sidebar chatbot, all behind one switch.

The short answer

Pick SigmaOS

if you want workspaces and tabs you mark done, on a Mac
if you browse by keyboard, with single-key shortcuts
if you prefer WebKit to Chromium and want spaces

Pick Firefox

if you want an open-source browser that isn’t Chromium
if you want AI off by default, or gone with one switch
if you want a free browser VPN, where it is offered

Or Yabours

if you miss Arc and want spaces, pins and folders kept, on a Mac
if you already pay for Claude or ChatGPT and want it to work in your signed-in tabs
if you want Claude Code, Codex or Cursor to drive a real browser over MCP

At a glance

SigmaOS and Firefox, with Yab beside them for a Mac.

SigmaOS vs Firefox
What	SigmaOS	Firefox	Yab
Made by	SigmaOS Inc. (London)	Mozilla	Serafim Korablev
Status	No release notes since February 2025	Updated	Updated
Runs on	Mac	Mac, Windows, Linux, iPhone and Android	Mac
Phone app	None; Mac only. iOS has been on its roadmap since 2021	iPhone, iPad and Android; syncs tabs, bookmarks, passwords and history	Not yet
Price	Free; Personal Pro $20/month or Personal Max $30/month for more AI	Free; its built-in VPN is free up to 50 GB a month	Free; its AI runs on your own Claude or ChatGPT plan
AI	Chat about pages, on its own AI service	Chat about pages, on its own AI or yours	An agent that works in pages, on your Claude or ChatGPT plan
Driven by outside agents	No	MCP	MCP and a command line
Engine	WebKit	Gecko	WebKit
Tabs down the side	Yes	A setting	Yes
Spaces	Yes	No	Yes
Split View	Yes	Yes	Yes
Extensions	Chrome Web Store	Firefox add-ons	Chrome Web Store
Ad blocker	Built in	No	Built in
Open source	No	Yes	No

Checked October 9, 2026 on each maker’s own pages, linked under Sources. Prices are per month, in US dollars.

Where they differ

What separates them, area by area. Where one plainly has more, it says who; where it comes down to taste, it says so.

AIa matter of taste

Both have AI to ask about pages, and neither does the clicking for you. Airis chats about the page you are on, sums it up, looks things up and translates; no agent. Firefox’s Smart Window beta chats with tabs you share and groups them, and a sidebar chatbot can use Claude, ChatGPT, Gemini, Le Chat or Copilot; it can’t click or fill forms, and one switch turns all AI off.

Agents like Claude Code and CodexFirefox leads

SigmaOS has no MCP server or command line for outside agents. Firefox can be driven over MCP, through Mozilla’s Firefox DevTools MCP, which starts its own Firefox.

Tabs and windowsSigmaOS leads

SigmaOS has tabs down the side, spaces and Split View. Firefox has tabs down the side as a setting, Split View, folders in the sidebar and tabs that sleep.

PriceFirefox leads

SigmaOS: Free; Personal Pro $20/month or Personal Max $30/month for more AI. Firefox: Free; its built-in VPN is free up to 50 GB a month.

Where it runsFirefox leads

SigmaOS runs on Mac. Firefox runs on Mac, Windows, Linux, iPhone and Android. On a Mac, SigmaOS needs macOS 12 or later and Firefox needs macOS 10.15 or later. SigmaOS has no phone app: Mac only. iOS has been on its roadmap since 2021. On the phone, Firefox: iPhone, iPad and Android; syncs tabs, bookmarks, passwords and history.

Engine and extensionsa matter of taste

SigmaOS is built on WebKit, the engine Safari uses; Firefox on Gecko, Firefox’s engine. SigmaOS takes extensions from the Chrome Web Store, Firefox from Firefox’s add-ons.

PrivacyFirefox leads

SigmaOS has an ad blocker built in. SigmaOS keeps history and cookies on your Mac unless you turn on sync, stored encrypted on AWS; its privacy policy doesn’t say where Airis requests go. Firefox has a VPN and open code. Smart Window sends prompts and what you share through Mozilla’s servers to partner models; Mozilla says it keeps no chat logs without permission and doesn’t train on them.

UpdatesFirefox leads

SigmaOS: Still downloadable, with no public release notes since version 1.19 in February 2025. Firefox is updated as usual.

What their pages don’t lead with

Real limits, from the makers’ own words and our own use.

SigmaOS

Mac only
No public release notes since version 1.19 in February 2025
Chrome extensions only partly work, behind its WebKit+ option
Its AI is an assistant, and regular use needs the $20 or $30 plans

Firefox

Its Smart Window AI is a beta in the US, Canada and France and needs a Mozilla account
Its AI can’t click, fill forms or buy for you
The free VPN covers the browser only, up to 50 GB a month, in a few countries
Firefox add-ons only, not the Chrome Web Store

Yab, honestly

Mac only: macOS 15.4 or later, no Windows, iPhone or Android
New: first released in September 2026
Its AI needs a Claude or ChatGPT plan; ChatGPT’s free plan may work with low limits
WebKit, as in Safari: a site tested only in Chrome can misbehave
Closed source

What changed lately

September 16, 2026Firefox: Smart Window beta expanded from the US and Canada to France
March 24, 2026Firefox: Firefox 149 added split view and a free built-in VPN
February 24, 2026Firefox: Firefox 148 added AI Controls with a switch that blocks all AI features
February 4, 2025SigmaOS: Version 1.19.0, a performance update, the last release with public notes

Questions

Is SigmaOS free?

Yes, with limits on its AI. Free; Personal Pro $20/month or Personal Max $30/month for more AI.

Is Firefox free?

Yes. Free; its built-in VPN is free up to 50 GB a month.

Which has an AI agent, SigmaOS or Firefox?

Neither has an agent that does tasks in your pages. Airis chats about the page you are on, sums it up, looks things up and translates; no agent. Firefox’s Smart Window beta chats with tabs you share and groups them, and a sidebar chatbot can use Claude, ChatGPT, Gemini, Le Chat or Copilot; it can’t click or fill forms, and one switch turns all AI off.

Which runs on Windows, SigmaOS or Firefox?

Firefox does. SigmaOS runs on Mac.

Do SigmaOS and Firefox have phone apps?

Firefox does. SigmaOS has no phone app: Mac only. iOS has been on its roadmap since 2021. On the phone, Firefox: iPhone, iPad and Android; syncs tabs, bookmarks, passwords and history.

Can I move from Firefox to SigmaOS?

Yes: SigmaOS’s own help says it brings in from Firefox.

Is SigmaOS still being updated?

Still downloadable, with no public release notes since version 1.19 in February 2025.

Is there a third option on a Mac?

Yab, Yet Another Browser, is free for the Mac: tabs down the side with spaces, folders and Split View, as in SigmaOS; an agent that works in your signed-in tabs, on the Claude or ChatGPT plan you already pay for. Claude Code, Codex and any MCP client can drive it too. It runs on WebKit, the engine Safari uses, and takes Chrome extensions. It is Mac only, and new.

More comparisons

SigmaOS vs Arc SigmaOS vs Vivaldi SigmaOS vs Zen SigmaOS vs Orion SigmaOS vs Chrome SigmaOS vs Safari SigmaOS vs Edge SigmaOS alternatives Yab vs SigmaOS Firefox vs Chrome Firefox vs Safari Firefox vs Edge Brave vs Firefox Opera vs Firefox Arc vs Firefox Dia vs Firefox Firefox alternatives Yab vs Firefox

Sources, read October 9, 2026. Something out of date? Write to hello@serafimlabs.io and we fix it.

Yab, Yet Another Browser.

Free for the Mac. Arc’s sidebar, your own Claude or ChatGPT as the agent, Chrome extensions on WebKit.

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