Firefox: focusmanager.testmode=true persists after browser close, breaking fcitx5 input method

[Quaop]

Description

When Playwright launches Firefox, it sets focusmanager.testmode = true in the user's Firefox profile. This pref is not cleaned up after Playwright exits, leaving it permanently in the user's normal Firefox profile.

This breaks fcitx5 (and likely other input method frameworks like IBus) in the user's daily browser, because focusmanager.testmode changes how focus events are dispatched, preventing the input method from properly receiving focus signals.

Steps to reproduce

1. Use Playwright to launch Firefox (persistent or non-persistent context)
2. Close Playwright
3. Open Firefox normally
4. Try using fcitx5/IBus input method (Ctrl+Space) → does not respond
5. Check about:config → focusmanager.testmode is true
6. Check prefs.js → contains user_pref("focusmanager.testmode", true);

Expected behavior

Playwright should:

• Either only set testmode prefs in temporary/isolated profiles (not the user's default profile)
• Or clean up testmode prefs when the browser context is closed

Actual behavior

focusmanager.testmode = true persists in the user's Firefox profile permanently, silently breaking input method functionality.

Environment

• Playwright Python 1.60.0
• Firefox 150.0.2 (Playwright-bundled)
• Gentoo Linux, XFCE4 (X11)
• fcitx5 5.1.19

Impact

Any Linux user who uses Playwright with Firefox and also uses fcitx5/IBus for CJK input will have their input method broken without any obvious cause. The user cannot reasonably connect "Playwright stopped working" to "my Chinese keyboard input is broken."

Workaround

Delete the pref from the user's Firefox profile:

sed -i '/focusmanager.testmode/d' ~/.mozilla/firefox/*.default*/prefs.js

Fix suggestion

Use a temporary/isolated profile for testmode prefs, or unset focusmanager.testmode on browser context close.

[yury-s]

Please provide exact steps, "Use Playwright to launch Firefox (persistent or non-persistent context)" is not specific enough. How exactly do you launch it, what user data dir do you pass? In non-persistent mode Playwright runs Firefox with an isolated profile and cannot interfere with your default profile, there must be something else.

[Quaop]

Thanks for the follow-up. You're right that my original report was imprecise — I had previously used channel="firefox" which likely introduced the pref into my default profile. However, I ran a clean reproduction today and the leak still occurs:

Reproduction script:

import asyncio
from playwright.async_api import async_playwright

async def main():
    async with async_playwright() as p:
        browser = await p.firefox.launch(headless=True)
        page = await browser.new_page()
        await page.goto("about:blank")
        await browser.close()

asyncio.run(main())

What I observed:

1. Before running: grep focusmanager ~/.mozilla/firefox/*.default*/prefs.js → clean
2. After running: focusmanager.testmode = true appeared in a system Firefox profile under ~/.mozilla/firefox/

Playwright's launch command was using the expected isolation flags:

firefox -no-remote -headless -profile /tmp/.../playwright_firefoxdev_profile-xxx -juggler-pipe -silent

So the pref shouldn't leak, but it does. This may be a Firefox upstream behavior where it still touches profiles registered in profiles.ini even when launched with -no-remote -profile.

Impact: This breaks fcitx5/IBus input method in the user's normal Firefox. Not Gentoo-specific — Firefox profile handling is upstream Mozilla behavior.

Workaround:

sed -i '/focusmanager.testmode/d' ~/.mozilla/firefox/*.default*/prefs.js

[Quaop]

Quick clarification on the reproduction: I should note that I only checked one profile before running the test, not all profiles under ~/.mozilla/firefox/. The leaked pref in the second profile may have been a leftover from earlier channel="firefox" usage rather than from this reproduction run.

So the confirmed trigger is channel="firefox" — when Playwright launches the system Firefox, focusmanager.testmode persists in the default profile after the session ends. I haven't reliably reproduced it without channel="firefox".

The core issue remains: Playwright sets this testing pref and it doesn't get cleaned up, which silently breaks input methods for Linux users who use channel="firefox".