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fix(chromium): restore automation launch flag #42403

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Devin Rousso (dcrousso) wants to merge 1 commit into from
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fix(chromium): restore automation launch flag #42403

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1 change: 1 addition & 0 deletions packages/playwright-core/src/server/chromium/chromiumSwitches.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,7 @@ export const chromiumSwitches = (options?: { android?: boolean }) => [
'--unsafely-disable-devtools-self-xss-warnings',
// Edge can potentially restart on Windows (msRelaunchNoCompatLayer) which looses its file descriptors (stdout/stderr) and CDP (3/4). Disable until fixed upstream.
'--edge-skip-compat-layer-relaunch',
'--enable-automation',

@yury-s Yury Semikhatsky (yury-s) Aug 27, 2026

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It was removed in this change after some back and forth changes. The idea was that when browser is controlled via remote debugger, the same features are already turned on. --enable-automation is a big hammer and we haven't heard any complaints after removing the flag. Let's narrow down what is not working in their scenario and see if we can fix it differently.

@dcrousso Devin Rousso (dcrousso) Aug 27, 2026

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unless im misreading the code, that change always set --enable-automation unless assistantMode: true, which was only for MCP, meaning that --enable-automation was always on for all other cases

furthermore, it was unconditionally added and has been unconditionally set since b20e87d 7yrs ago

@dcrousso Devin Rousso (dcrousso) Aug 27, 2026

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as the original issue demonstrates, Chromium also uses --enable-automation to disable process handoff behavior https://issues.chromium.org/issues/371112535

// This disables Chrome for Testing infobar that is visible in the persistent context.
// The switch is ignored everywhere else, including Chromium/Chrome/Edge.
'--disable-infobars',
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8 changes: 8 additions & 0 deletions packages/playwright-core/src/tools/mcp/browserFactory.ts
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Expand Up @@ -90,11 +90,18 @@ async function createIsolatedBrowser(config: FullConfig, clientInfo: ClientInfo)
testDebug('create browser (isolated)');
const browserType = playwright[config.browser.browserName];
const tracesDir = await computeTracesDir(config, clientInfo);
const configIgnoreDefaultArgs = config.browser.launchOptions?.ignoreDefaultArgs;
const browser = await browserType.launch({
tracesDir,
...config.browser.launchOptions,
handleSIGINT: false,
handleSIGTERM: false,
ignoreDefaultArgs: configIgnoreDefaultArgs === true
? true
: [
'--enable-automation',
...Array.isArray(configIgnoreDefaultArgs) ? configIgnoreDefaultArgs : [],
],
}).catch(error => {
throwIfExecutableMissing(error, config);
throw error;
Expand Down Expand Up @@ -175,6 +182,7 @@ async function createPersistentBrowser(config: FullConfig, clientInfo: ClientInf
? true
: [
'--disable-extensions',
'--enable-automation',
...Array.isArray(configIgnoreDefaultArgs) ? configIgnoreDefaultArgs : [],
],
};
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