> ## Documentation Index
> Fetch the complete documentation index at: https://docs.browspark.krishm.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Using multiple browsers

> Connect Chrome, Brave, Firefox and Zen profiles and developer sessions through one companion.

Browspark can use Chrome, Brave, Firefox and Zen at the same time. All browsers share one companion and the same 43 MCP tools. Each tab has a unique `tabId`, so a command always goes to the selected browser and tab.

| Browser                 | Your existing tabs                                 | Separate developer session               |
| ----------------------- | -------------------------------------------------- | ---------------------------------------- |
| Chrome                  | Install the extension and share tabs               | `browser: "chrome"`                      |
| Brave                   | Install the extension and share tabs               | `browser: "brave"`                       |
| Firefox                 | Firefox 153+ with the Firefox extension            | `browser: "firefox"`                     |
| Zen                     | Firefox extension on a build based on Firefox 153+ | `browser: "zen"`                         |
| Other Chromium browsers | Install the extension where supported              | `browser: "chromium"` with `browserPath` |

Firefox and Zen have [documented tool exceptions](/reference/firefox). Their extension shares everyday tabs; their developer sessions use WebDriver BiDi with separate profiles and broader automation support.

## Connect existing browser profiles

1. [Register the companion](/get-started/quickstart) once with your MCP client.
2. Load the Browspark extension in Chrome at `chrome://extensions` and Brave at `brave://extensions`. You can use the same unpacked extension folder in both.
   For Firefox and Zen, build and load the separate Firefox package through `about:debugging`, then enable user scripts in its dashboard. See [Firefox extension setup](/reference/firefox#install-the-firefox-extension).
3. Open each dashboard and share the tabs you want the agent to access. Every browser profile connects to `127.0.0.1:9223`, or the port you configured.
4. Ask the agent to call `browser_status` or `browser_tabs`. Connected extension instances have a `browserId`; their tabs have unique `tabId` values.

Connecting Brave keeps Chrome connected. Multiple profiles of the same browser can also connect independently. Sharing a tab in one profile grants no access to tabs in another, and its Stop controls affect that profile's tabs.

Open [Graph](/dashboard/graph) in any connected dashboard to arrange the agents, companion, browser profiles and developer sessions on a dotted canvas with logos and animated lines. Extension nodes include shared-tab counts; developer nodes show open-tab counts. **Settings → Connection graph** controls this view for that profile. Recognized logos and engine fallback names identify connections; they do not guarantee support for every browser fork.

Use companion 0.5.0 or later for Chromium extensions, or 0.6.0 or later for Firefox extensions. When testing extensions built from source, run the companion from the same checkout and restart any older companion already using the port. See [connection troubleshooting](/guides/troubleshooting#browsers-alternate-between-connected-and-disconnected).

Profiles with copied extension storage remain independent: connections are identified by both installation and browser session, so a copied installation ID cannot disconnect another running browser session.

## Choose where a new tab opens

For a connected extension browser, use its displayed `browserId` with `browser_tabs`:

```json theme={null}
{
  "action": "new",
  "mode": "extension",
  "browserId": "<browserId from browser_status>",
  "url": "https://example.com"
}
```

Replace the placeholder with the value returned by the tool. Browser IDs identify connections, so copy the returned ID instead of guessing one from a browser name. When multiple browsers are connected, specify your choice; Browspark will not pick whichever connected last.

For an existing tab, pass its `tabId` to `browser_navigate`, `browser_snapshot` or another tab tool. A `tabId` already identifies the browser; it does not need an extra `browserId`.

The dashboard displays browser-native tab numbers, which differ from MCP tab IDs. Refresh `browser_status` after restarting the companion or browser instead of reusing old IDs.

`browser_fetch` also accepts `browserId` when it opens temporary tabs in an extension browser. Pass the ID from `browser_status` to choose which browser performs the fetch; pass `context` to use a developer browser instead.

## Run developer browsers side by side

Ask your agent to launch the browsers you need, each in a named context. Active context names must be unique across browsers. For example, launch Brave with:

```json theme={null}
{
  "action": "launch",
  "browser": "brave",
  "context": "brave-work",
  "userRequested": true
}
```

Then launch Zen with:

```json theme={null}
{
  "action": "launch",
  "browser": "zen",
  "context": "zen-work",
  "userRequested": true
}
```

These are `browser_session` calls. Use `"chrome"` or `"firefox"` for those browsers. The existing `"chromium"` choice remains supported and is the default for a new context.

Use `context` to open a new tab in a developer browser:

```json theme={null}
{
  "action": "new",
  "mode": "dev",
  "context": "zen-work",
  "url": "https://example.com"
}
```

Developer profiles persist separately by browser and context. Closing a context keeps its profile; `browser_session` with `action: "delete"` removes a stopped profile. See [developer browser profiles and options](/concepts/developer-browser).

## Sharing and tool settings

Each extension profile owns its shared tabs, overlay setting and Stop controls. A tool call targeting an extension browser or tab uses that browser's tool switches, including page tools that resolve to the agent's own or only usable tab. Calls spanning browsers and calls in developer sessions use the combined disabled list from connected dashboards.

Developer launches use the most restrictive connected dashboard setting: **Never**, then **Only when needed**, then **Always**. See [Tool policy](/concepts/tool-policy) for details.

## Select an executable

Set `browserPath` on `browser_session launch` when a browser is installed outside the usual locations. Keep `browser` set to the matching browser so the companion uses the correct protocol and profile.

The environment variables `BROWSPARK_CHROME`, `BROWSPARK_BRAVE`, `BROWSPARK_FIREFOX` and `BROWSPARK_ZEN` select the corresponding executable. Existing `chromePath` and `firefoxPath` launch options remain supported. See [CLI and environment](/reference/cli-and-environment).