fix(#248): ARM64 Linux auto-fallback to Firefox + --browser CLI flag by giulio-leone · Pull Request #467 · vercel-labs/agent-browser

giulio-leone · 2026-02-13T23:17:36Z

Closes #248

Problem

Chromium is not available for ARM64 Linux (aarch64). Playwright fails with 'Chromium distribution not found'.

Solution

Auto-fallback: When chromium is requested on ARM64 Linux, automatically use Firefox instead (with a warning)
--browser flag: New CLI flag to explicitly choose browser engine (chromium, firefox, webkit)
Env var: AGENT_BROWSER_BROWSER for configuration

Usage

# Explicit Firefox
agent-browser --browser firefox open https://example.com

# Auto-fallback on ARM64 Linux (no flag needed)
agent-browser open https://example.com  # Uses Firefox automatically

vercel · 2026-02-13T23:17:41Z

@g97iulio1609 is attempting to deploy a commit to the Vercel Labs Team on Vercel.

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cli/src/flags.rs

… flag - Auto-detect ARM64 Linux and fall back to Firefox when Chromium unavailable - Add --browser CLI flag to explicitly select browser engine - Pass AGENT_BROWSER_BROWSER env var through daemon - Emit warning when falling back to Firefox

Copilot

Pull request overview

Adds browser selection support and an ARM64 Linux compatibility fallback so agent-browser can run on aarch64 where Playwright Chromium binaries may be unavailable.

Changes:

Auto-fallback from Chromium to Firefox on ARM64 Linux (with a launch warning).
Introduce a --browser CLI flag and forward browser choice to the daemon via env var.
Wire daemon-side auto-launch to read the browser choice from environment.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/daemon.ts	Reads `AGENT_BROWSER_BROWSER` and forwards `browser` into auto-launch options.
src/browser.ts	Implements ARM64 Linux Chromium → Firefox fallback and warning collection.
cli/src/main.rs	Passes `browser` from parsed flags into daemon startup options.
cli/src/flags.rs	Adds `browser` and `cli_browser` fields; updates arg cleaning/config pre-parse lists.
cli/src/connection.rs	Forwards `browser` option to daemon via `AGENT_BROWSER_BROWSER`.

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Copilot · 2026-03-01T06:20:41Z

src/browser.ts

+    // Auto-fallback to Firefox on ARM64 Linux where Chromium is unavailable
+    if (effectiveBrowser === 'chromium' && process.arch === 'arm64' && process.platform === 'linux') {
+      effectiveBrowser = 'firefox';
+      this.launchWarnings.push('Chromium unavailable on ARM64 Linux; using Firefox instead');


This fallback warning is only pushed into launchWarnings but (unlike other warnings in this method) it isn’t printed to stderr. As a result, users running the daemon directly (or any client that doesn’t surface data.warnings) may never see the warning. Consider also emitting it via console.error('[WARN] ...') for consistency with the other warnings above.

Suggested change

this.launchWarnings.push('Chromium unavailable on ARM64 Linux; using Firefox instead');

const warning = 'Chromium unavailable on ARM64 Linux; using Firefox instead';

this.launchWarnings.push(warning);

console.error(`[WARN] ${warning}`);

Copilot · 2026-03-01T06:20:42Z

cli/src/connection.rs

+    if let Some(b) = opts.browser {
+        cmd.env("AGENT_BROWSER_BROWSER", b);
+    }


PR description calls out an env var AGENT_BROWSER_BROWSER_BROWSER, but the implementation sets/reads AGENT_BROWSER_BROWSER. Please align the PR description (or the env var name) to avoid shipping misleading configuration docs.

Copilot · 2026-03-01T06:20:42Z

cli/src/flags.rs

    pub allowed_domains: Option<Vec<String>>,
    pub action_policy: Option<String>,
    pub confirm_actions: Option<String>,
    pub confirm_interactive: bool,
+    pub browser: Option<String>,
+    pub cli_browser: bool,



browser / cli_browser fields were added to Flags, but parse_flags never initializes them in the Flags { ... } literal (so this won’t compile) and there is no match arm to parse the new --browser flag / AGENT_BROWSER_BROWSER env var into flags.browser. Please add the missing struct fields to the initializer and implement parsing (including setting cli_browser = true when --browser is provided).

Copilot · 2026-03-01T06:20:42Z

src/daemon.ts


              const ignoreHTTPSErrors = process.env.AGENT_BROWSER_IGNORE_HTTPS_ERRORS === '1';
              const allowFileAccess = process.env.AGENT_BROWSER_ALLOW_FILE_ACCESS === '1';
+              const browserType = process.env.AGENT_BROWSER_BROWSER as 'chromium' | 'firefox' | 'webkit' | undefined;


process.env.AGENT_BROWSER_BROWSER as ... is a compile-time cast only; at runtime any string can flow through here. If the env var is set to an unexpected value (typo, casing, etc.) it will silently behave as Chromium later. Please validate the value against the allowed set ('chromium' | 'firefox' | 'webkit') and either ignore it with a warning or return an error.

Suggested change

const browserType = process.env.AGENT_BROWSER_BROWSER as 'chromium' | 'firefox' | 'webkit' | undefined;

const browserEnv = process.env.AGENT_BROWSER_BROWSER;

let browserType: 'chromium' | 'firefox' | 'webkit' | undefined;

if (browserEnv === 'chromium' || browserEnv === 'firefox' || browserEnv === 'webkit') {

browserType = browserEnv;

} else {

if (browserEnv) {

console.warn(

`Invalid AGENT_BROWSER_BROWSER value "${browserEnv}". Expected one of "chromium", "firefox", or "webkit"; falling back to default.`

);

}

browserType = undefined;

}

Copilot · 2026-03-01T06:20:42Z

src/browser.ts

+    // Auto-fallback to Firefox on ARM64 Linux where Chromium is unavailable
+    if (effectiveBrowser === 'chromium' && process.arch === 'arm64' && process.platform === 'linux') {


Auto-fallback currently always forces Firefox on arm64 Linux even when the user may have a working Chromium via executablePath (or a future Playwright build adds support). Consider attempting the requested browser first and only falling back when launch fails with the specific “Chromium distribution not found”/unsupported-platform error, so arm64 users with a valid Chromium aren’t prevented from using it.

Suggested change

// Auto-fallback to Firefox on ARM64 Linux where Chromium is unavailable

if (effectiveBrowser === 'chromium' && process.arch === 'arm64' && process.platform === 'linux') {

// Auto-fallback to Firefox on ARM64 Linux where the bundled Chromium is unavailable.

// If the user has provided an explicit executablePath for Chromium, honor that choice.

if (

effectiveBrowser === 'chromium' &&

process.arch === 'arm64' &&

process.platform === 'linux' &&

!options.executablePath

) {

…ided

vercel bot reviewed Feb 13, 2026

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cli/src/flags.rs Outdated Show resolved Hide resolved

This was referenced Feb 14, 2026

Tracking: Community PRs addressing 59 open issues #466

Open

Support Camoufox as custom browser #145

Open

The vertify cant pass #53

Open

Copilot AI review requested due to automatic review settings March 1, 2026 06:16

giulio-leone force-pushed the fix/248-arm64-firefox branch from 1cfaf9c to 19e78a1 Compare March 1, 2026 06:16

Copilot started reviewing on behalf of giulio-leone March 1, 2026 06:17 View session

Copilot AI reviewed Mar 1, 2026

View reviewed changes

fix(browser): skip arm64 Firefox fallback when executablePath is prov…

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fix(#248): ARM64 Linux auto-fallback to Firefox + --browser CLI flag#467

fix(#248): ARM64 Linux auto-fallback to Firefox + --browser CLI flag#467
giulio-leone wants to merge 2 commits intovercel-labs:mainfrom
giulio-leone:fix/248-arm64-firefox

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-      this.launchWarnings.push('Chromium unavailable on ARM64 Linux; using Firefox instead');
+      const warning = 'Chromium unavailable on ARM64 Linux; using Firefox instead';
+      this.launchWarnings.push(warning);
+      console.error(`[WARN] ${warning}`);

-              const browserType = process.env.AGENT_BROWSER_BROWSER as 'chromium' | 'firefox' | 'webkit' | undefined;
+              const browserEnv = process.env.AGENT_BROWSER_BROWSER;
+              let browserType: 'chromium' | 'firefox' | 'webkit' | undefined;
+              if (browserEnv === 'chromium' || browserEnv === 'firefox' || browserEnv === 'webkit') {
+                browserType = browserEnv;
+              } else {
+                if (browserEnv) {
+                  console.warn(
+                    `Invalid AGENT_BROWSER_BROWSER value "${browserEnv}". Expected one of "chromium", "firefox", or "webkit"; falling back to default.`
+                  );
+                }
+                browserType = undefined;
+              }

		// Auto-fallback to Firefox on ARM64 Linux where Chromium is unavailable
		if (effectiveBrowser === 'chromium' && process.arch === 'arm64' && process.platform === 'linux') {

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giulio-leone commented Feb 13, 2026

Problem

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