Firefox 140 and newer
Anthropic, Google and OpenAI all put their browser agents in Chrome and stop there. Browsentic is a Firefox add-on, signed by Mozilla, with a side panel that runs on whichever of those agents is already on your machine.
Pick the agent
None of these vendors has a Firefox add-on, and none of them is likely to. They do all have a command line tool, which is the half Browsentic needs.
Claude in Chrome is exactly what its name says, and there is no Firefox edition of it. Browsentic is the way a Firefox tab reaches Claude: the add-on hands the page to the Claude Code CLI you already run, on the plan you already have.
Gemini in Chrome is built into Chrome and goes no further. Antigravity, Google’s agent CLI, runs Gemini on your own machine, and Browsentic points it at the Firefox tab in front of you.
OpenAI’s browser work lives in ChatGPT and a Chrome extension. The Codex CLI has no such boundary, so it drives Firefox here on the ChatGPT plan you already pay for.
Mistral’s CLI, on the same footing as the others. Beta here while its session handling settles, so expect the odd retry on a long run.
xAI’s CLI, also beta. It works; it has had less mileage in the panel than Claude Code and Codex have.
What Firefox does differently
The differences are real and worth knowing before you install, so here they are, including the one that costs you something.
Mozilla signs the build, so Firefox installs it for good. Anything loaded through about:debugging is gone at the next restart. This is not that: it survives restarts like any other add-on.
Firefox checks the release page for a newer signed build about once a day and updates on its own. Check for Updates under the gear in about:addons does it now. There is no reload arrow and nothing to press, which Chrome cannot say.
The trusted click, both captcha tools, the four diagnostics tools and the two page-code tools are built on Chrome’s DevTools Protocol, which Firefox does not expose. The Firefox build leaves them off the list it publishes, so the agent never sees them and never plans around them. A stale recording that names one gets UNSUPPORTED with a hint, rather than failing quietly.
It drives the real tab you are looking at, with the cookies, the container and the two-factor state it already has. Nothing is re-authenticated anywhere, because nothing new is launched.
Install
Release Firefox installs only add-ons that addons.mozilla.org has signed, so the Firefox build is not a folder you load. It is a signed .xpi attached to every GitHub release.
01
It starts the daemon and prints two things: a link to the signed add-on for that exact version, and a pairing code. On a Mac the app starts the same daemon, and you take the add-on from the release page.
npx browsentic setup --browser firefox02
Accept both prompts: one to let github.com install software, one to add Browsentic. Firefox shows you what the add-on asks for. Prefer the file? Download the .xpi, open about:addons, press the gear and choose Install Add-on From File.
about:addons03
Into the popup, then press Connect. Single use, ten minutes, and the session key it hands back survives restarts. Run browsentic pair if you need another.
npx browsentic pairIf the command says the file is not attached yet, Mozilla is still signing that version. It usually appears within minutes.
Questions
Not from Anthropic. Claude in Chrome is Chrome only. Browsentic is a Firefox add-on that runs Claude Code, the CLI you already have on your machine, against the Firefox tab in front of you. The reasoning happens locally on your existing plan, with no API key.
Through Antigravity, yes. Google’s Gemini in Chrome feature is part of Chrome and does not come to Firefox, but Antigravity is Google’s agent CLI and runs on your machine. Install it, log in once, pick it in the Browsentic popup, and the Firefox side panel is Gemini.
It is signed by Mozilla, on the unlisted channel, and attached to each GitHub release instead of being listed in the store. The reason is that the add-on and the local daemon ship as one version and have to stay in step, which a store listing on its own review clock cannot guarantee. Firefox still verifies the signature, still shows you the permissions, and still updates it for you.
Firefox 140 or newer, on macOS, Windows or Linux. Developer Edition and Nightly can also load the unsigned build from a source checkout, which is the loop for working on Browsentic rather than for using it.
Nine of the 41 tools. The trusted click, the two captcha tools, the four diagnostics tools and the two page-code tools all need the DevTools Protocol, which is a Chrome thing. Everything else is the same: reading the page as structure, clicking, typing, navigating, screenshots, tabs, recordings, site maps and WebMCP.
Free and MIT licensed. No signup, no key to paste, and a fresh install connects to nothing until you pair it yourself.
npx browsentic setup