fix: open Firefox and Chromium when running in WSL by Seismix · Pull Request #2055 · wxt-dev/wxt

Seismix · 2026-01-27T09:45:53Z

Overview

Rebased onto the new runner structure (#2647, #2651). Instead of refusing to open a browser in WSL, WebExtRunner.openBrowser() now lets web-ext open Firefox and Chromium installed inside WSL. It falls back to the manual-load message when:

There's no display. WSL sets DISPLAY/WAYLAND_DISPLAY only when GUI apps are enabled (WSLg), as discussed in WSL runner should check DISPLAY env var before refusing to open browser (WSLg support) #1931.
Only a Windows Chromium is available. WSL can't pass Chromium's remote debugging pipe (fds 3 and 4) to Windows processes. WXT looks for a Linux Chromium on the PATH the way chrome-launcher does, or uses binaries.chrome.
Firefox or Chromium is a Snap (Ubuntu's default). Its sandbox can't read web-ext's temporary profile in /tmp, unless TMPDIR is inside the home directory.

Removing the isWsl check isn't enough for Chromium: chrome-launcher rewrites --user-data-dir into a Windows UNC path in WSL (GoogleChrome/chrome-launcher#334). Chromium then creates a \\wsl.localhost\... folder in the project and ignores WXT's default prefs. WXT creates the profile itself and passes --user-data-dir again, keeping a user's own. This can be removed once GoogleChrome/chrome-launcher#360 is released.

My earlier description was wrong: the UNC path doesn't break the debugging pipe. Launching failed because chrome-launcher picked the Windows Chrome.

Docs: a new WSL section in Browser Startup, linked from the warnings.

Manual Testing

WSL2 + WSLg, Ubuntu 22.04, with Chrome 155 and Firefox 157 (deb and Snap) installed inside WSL.

Scenario	Result
`bun run dev` in `wxt-demo`	Chrome opens with the extension. No `\\wsl.localhost` folder; profile removed on Ctrl+C
`chromiumArgs: ['--user-data-dir=...']`	User's profile used and kept
`DISPLAY` and `WAYLAND_DISPLAY` unset	Display warning, no launch
`bun run dev:firefox`, Snap Firefox	Snap warning, no launch
`bun run dev:firefox`, non-Snap Firefox	Firefox opens with the extension
Real project with `binaries.chrome` and `chromiumArgs`	Configured Chrome opens with the extension

Related Issue

This PR closes #1931

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Seismix · 2026-01-29T07:48:36Z

packages/runner/src/install.ts uses the using keyword (Explicit Resource Management):

wxt/packages/runner/src/install.ts

Line 14 in 83decf7

using bidi = await createBidiConnection(debuggerUrl);

During development these build failures weren't happening because of a Node version mismatch between my env and the CI env.
CI runs Node 22 which doesn't support this without the --js-explicit-resource-management flag. Node 24 has it enabled by default, which is why it worked locally for me.

As far as I can tell, previous builds had @wxt-dev/runner cached. My changes to browser-paths.ts invalidated that cache, so now it actually tries to rebuild and fails.

Can I get input on this? I marked the PR as draft in the meantime.

PatrykKuniczak · 2026-02-08T16:43:46Z

@Seismix Let's rebase in the near future because we'll have changes aroud runner in #2079
This can help you or you'll need to change your approach.

Anyway node 24 should be supported by us, because it was the newest LTS version.
If you need to use v24, feel free to open PR, where you change necessary version from 18 to 24, here:

wxt/package.json

Lines 4 to 6 in 1fe0730

    
           "engines": { 
        
             "node": ">=18.20.3" 
        
           },

I hope @aklinker1 won't have any arguments to block this change, but we'll see 😆

aklinker1 · 2026-02-09T08:20:04Z

This has gone way beyond the amount of work I thought was required based off the issue discussion...

Let's pause for a second, does web-ext support WSL? If so, just remove this if-statement:

wxt/packages/wxt/src/core/runners/index.ts

Line 12 in 75f01db

if (isWsl()) return createWslRunner();

If not, add support for WSL over there: https://github.com/mozilla/web-ext

WXT relies on web-ext to open the browser, seems like this work should go there, not in WXT.

Ignore the @wxt-dev/runner package for now, it's not ready for use.

Seismix · 2026-02-09T19:25:48Z

You're right @aklinker1 , web-ext does partially support WSL. After testing on WSL2 + WSLg:

Firefox: Works out of the box via web-ext. wxt dev -b firefox launches Firefox and installs the extension with no issues.
Chrome: web-ext run -t chromium by itself does launch Chrome and load the extension, but it still creates a malformed UNC profile path (\\wsl.localhost\...) due to chrome-launcher. There's no web-ext flag to prevent this. The conversion happens unconditionally inside chrome-launcher. When used through WXT's programmatic API (web-ext-run), this causes an ECONNRESET crash on the CDP pipe.

The work on the wsl-runner branch was trying to work around the following bugs. But it makes more sense to fix them at the source.

Investigation

There are two upstream bugs at play:

chrome-launcher unconditionally converts --user-data-dir to a Windows UNC path (\\wsl.localhost\...) when it detects WSL:
https://github.com/GoogleChrome/chrome-launcher/blob/fe7654fbfd1ed651be9d576b6b46592b70e5b693/src/chrome-launcher.ts#L198
Even when Chrome is running as a native Linux process under WSLg. This causes Chrome's remote debugging pipe to reset. Known upstream:

web-ext-run doesn't attach an error handler to the outgoing CDP pipe https://github.com/aklinker1/web-ext-run/blob/master/src/extension-runners/chromium.js#L67, compared with the incoming pipe which has error handling at https://github.com/aklinker1/web-ext-run/blob/master/src/extension-runners/chromium.js#L57. When the pipe resets, it becomes an unhandled 'error' event that crashes the Node.js process.

Possible solutions

Minimal: Remove the WSL runner, warn for Chromium: Delete the old WSL runner (which was a no-op for all browsers anyway), let Firefox go through web-ext normally, and show a warning + manual fallback for Chromium in WSL until the upstream bugs are fixed. Possibly drop the is-wsl dependency (use an inline /proc/version check instead).

Patch dependencies via pnpm: Apply pnpm patch to both chrome-launcher (skip toWin32Path() when a GUI display is available) and web-ext-run (add error handler on the outgoing CDP pipe). This would make Chrome work in WSL immediately without waiting for upstream fixes:

possible chrome-launcher fix:

const hasDisplay = process.env.DISPLAY || process.env.WAYLAND_DISPLAY;
flags.push(
  `--user-data-dir=${isWsl && !hasDisplay ? toWin32Path(this.userDataDir) : this.userDataDir}`,
);

possible web-ext-run fix:

outgoing.on('error', error => {
  log.error(error);
  this.#finalizeDisconnect();
});
outgoing.on('close', () => this.#finalizeDisconnect());

Fix upstream + option 1 as interim: Submit PRs to chrome-launcher and web-ext-run, use option 1 in WXT as a temporary measure, and remove the WSL check entirely once the upstream fixes land.
Combinations?

Branches

I've created branches for demonstration purposes:

Option 1: main...Seismix:wxt:wsl/remove-runner : minimal change, warns for Chromium, Firefox works
Option 2: main...Seismix:wxt:wsl/patch-deps : patches both deps + wrapper script detection, both browsers work

What next

How should I move forward?

aklinker1 · 2026-02-09T19:52:56Z

I like option 3 - interim solution + upstream support.

PatrykKuniczak · 2026-04-12T20:14:31Z

@Seismix Are you want to go on?

PatrykKuniczak · 2026-04-24T08:54:14Z

@Seismix One more poke :)

Seismix · 2026-04-27T11:46:15Z

Hey @PatrykKuniczak, I will pick this up again. Busy times, sorry for the break.

PatrykKuniczak · 2026-04-27T17:08:34Z

@Seismix No problem, take your time.
I only need to know, if you're interested on continue working on this :)

sarod · 2026-10-02T15:55:24Z

.

Hi @Seismix do you still plan to work on this?

coderabbitai · 2026-10-02T22:12:46Z

📝 Walkthrough

Walkthrough

WSL runner selection now distinguishes Chromium from Firefox. The resolver uses the WSL Snap Firefox runner only when detection identifies the configured Firefox binary as unusable. Other WSL Firefox cases continue through the existing web-ext loading and fallback flow. WSL runner warnings give browser-specific instructions.

Changes

WSL browser runner selection

Layer / File(s)	Summary
WSL runner reasons and Snap detection `packages/wxt/src/core/runners/wsl.ts`, `packages/wxt/src/core/runners/__tests__/wsl.test.ts`	`createWslRunner` accepts a browser-specific reason and logs matching instructions. Snap Firefox detection checks paths and launcher content. Tests cover Snap binaries, symlinks, the Ubuntu shim, `PATH` lookup, and non-Snap or missing binaries.
Browser-specific runner routing `packages/wxt/src/core/resolve-config.ts`, `packages/wxt/src/core/utils/wsl.ts`, `packages/wxt/e2e/tests/runners.test.ts`	In WSL, non-Firefox browsers use the Chromium runner. Firefox uses the Snap Firefox runner only when detection identifies an unusable Snap installation; other cases continue through the existing `web-ext` flow. E2E tests cover these selections, and the `isWsl()` utility file is removed.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant resolveRunner
  participant isUnusableSnapFirefox
  participant createWslRunner
  participant web-ext
  resolveRunner->>createWslRunner: Select Chromium runner for other WSL browsers
  resolveRunner->>isUnusableSnapFirefox: Check configured Firefox binary in WSL
  isUnusableSnapFirefox-->>resolveRunner: Return Snap Firefox usability result
  alt Snap Firefox is unusable
    resolveRunner->>createWslRunner: Select snap-firefox runner
  else Other Firefox installation or outside WSL
    resolveRunner->>web-ext: Continue existing loading and fallback flow
  end

Merge Risk: 🟡 Moderate · up to 18cfb

On WSL, some Snap Firefox setups will not get the intended workaround warning. Firefox will fail to launch without explanation. Fix the Snap detection before merging.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
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Description check		The description includes the required Overview, Manual Testing, and Related Issue sections. It explains the WSL behavior, test scenarios, limitations, and closes issue `#1931`.
Title check		The title clearly and concisely describes the main change: enabling Firefox and Chromium startup behavior in WSL.

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Seismix · 2026-10-02T22:16:28Z

@sarod @PatrykKuniczak sorry for the long silence, I picked this back up.

@aklinker1 I rebuilt it as the option 3 interim fix, on top of 0.21. The old runner work is gone, and the diff is now mostly in resolveRunner():

Firefox goes straight through web-ext in WSL. Chromium still gets a warning, now linking the chrome-launcher bug.
The second commit warns when Firefox is the Snap build, which is what Ubuntu WSL installs by default. Its sandbox can't read web-ext's temp profile, so without the check you get a "profile cannot be loaded" popup and ECONNREFUSED.

I tested both browsers on WSLg, with Snap and non-Snap Firefox. Details are in the PR description.

For the upstream part: GoogleChrome/chrome-launcher#360 already fixes the UNC path problem and checks for a Windows binary, which works better than the DISPLAY check I suggested earlier. I'll back that PR with a repro. web-ext has the same missing error handler on the outgoing debugging pipe that web-ext-run had. Once these are fixed upstream, the Chromium warning can go.

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commit: 18cfbc3

codecov · 2026-10-11T11:32:03Z

Codecov Report

❌ Patch coverage is 87.87879% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.69%. Comparing base (d718668) to head (18cfbc3).
⚠️ Report is 41 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/wxt/src/core/runners/wsl.ts	86.20%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2055      +/-   ##
==========================================
+ Coverage   79.55%   79.69%   +0.14%     
==========================================
  Files         135      134       -1     
  Lines        4054     4083      +29     
  Branches      944      956      +12     
==========================================
+ Hits         3225     3254      +29     
  Misses        733      733              
  Partials       96       96

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Inline comments:
Review comments at @packages/wxt/src/core/runners/wsl.ts:
- Around line 40-41: In resolveRunner, check the original launcher path for
`/snap/` before calling realpath, so symlinks such as `/snap/bin/firefox` are
recognized before resolution; retain the resolved-path check for other Snap
layouts. Add coverage for a launcher symlink that points to a Snap command
outside the Snap tree.
- Line 36: Update the path selection in the Snap Firefox detection flow so
configured command aliases are resolved through PATH before realpath, while
configured paths containing a slash are preserved. Use the existing binary
value, falling back to the Firefox command name when unset.

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PatrykKuniczak · 2026-10-11T11:36:41Z

@Seismix Thanks for your contribution, but we need to wait for @aklinker1 approval, because he requested changes 😄
Good luck

aklinker1 · 2026-10-11T13:19:47Z

Conflicts need resolved, this code was recently moved around.

`web-ext` opens Firefox and Chromium installed inside WSL, so only fall back to the manual message when it can't: - No display: WSL only sets `DISPLAY` and `WAYLAND_DISPLAY` when GUI apps are enabled (WSLg), and browsers can use either one. - Chromium installed on Windows: WSL can't pass Chrome's remote debugging pipe (file descriptors 3 and 4) to Windows processes. A Linux Chromium is found on the `PATH` like `chrome-launcher` does, or configured with `binaries`. - Snap Firefox and Chromium: the sandbox can't read the temporary profile in `/tmp`, unless `TMPDIR` is inside the home directory. `chrome-launcher` rewrites `--user-data-dir` into a Windows UNC path in WSL (GoogleChrome/chrome-launcher#334), so WXT creates the Chromium profile and passes `--user-data-dir` again. A user's own `--user-data-dir` is kept. Closes wxt-dev#1931

Seismix · 2026-10-11T19:59:13Z

@aklinker1 Conflicts resolved. It now also opens a Chromium installed inside WSL, and checks for a display as discussed in #1931. Details are in the description.

Seismix requested review from Timeraa and aklinker1 as code owners January 27, 2026 09:45

Seismix marked this pull request as draft January 29, 2026 07:29

aklinker1 force-pushed the main branch from db3e29d to adaae6e Compare February 22, 2026 23:30

Seismix force-pushed the wsl-runner branch from 038015e to 18cfbc3 Compare October 2, 2026 22:12

Seismix changed the title ~~feat: enable native browser launching in WSL with GUI support~~ fix: allow opening Firefox in WSL Oct 2, 2026

Seismix marked this pull request as ready for review October 2, 2026 22:14

Seismix requested review from PatrykKuniczak and nishu-murmu as code owners October 2, 2026 22:14

coderabbitai Bot reviewed Oct 11, 2026

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Comment thread packages/wxt/src/core/runners/wsl.ts Outdated

Comment thread packages/wxt/src/core/runners/wsl.ts Outdated

Seismix force-pushed the wsl-runner branch from 18cfbc3 to ea874ee Compare October 11, 2026 19:58

Seismix changed the title ~~fix: allow opening Firefox in WSL~~ fix: open Firefox and Chromium when running in WSL Oct 11, 2026

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Overview

Manual Testing

Related Issue

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Investigation

Possible solutions

Branches

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