Firefox Community Forum

Hello,

I have the following error message......."The Application has failed to start because its side-by-side configuration is incorrect. Please see the application event log or use the command-line sestrace.exe tool for more detail?

This error message pops up when I click on the Firefox icon. How do I correct this error message?

Thank you.

Moin, seit einigen Tagen startet Firefox bei Klick auf das Symbol in der Taskleiste nicht. Wenn ich mehrmals klicke erscheint Firefox soviele Male wie geklickt. Mein System: Win11 25H2. Kann jemand helfen?

Since the latest Firefox update, it hangs immediately at startup. Now it never works, while other browsers always work. This is a fully updated Windows 10 computer. Even when it does work, Firefox's special tabs - About, Close Firefox, Restore session - are often big trouble; and it seems possible one of these may be the problem now. When Firefox is working. it either closes slowly or not at all, bringing always problematic "Firefox is already running - Close Firefox" messages. When one Firefox window is closed, Firefox always keeps the window that is causing trouble in the first place. So, two things. 1) Firefox doesn't work at all. If you fix this problem with an update, the update must start immediately because clicking on "Download Update" too will be hung. 2) You have terribly problematic special tabs which I have named above. It is my opinion that you cannot fix them - you have to rebuild them from scratch - otherwise they would be working properly right now. I have fallen back on Microsoft Edge which always works. Firefox is never working. Think about it.

When I open Firefox, I get Welcome to Firefox each time. I asked this question earlier and received this response:

This sounds like Firefox is not saving the profile/setup changes between launches. I’d check that Firefox isn’t running in a temporary/new profile and that the profile folder is writable.

You could also try creating a new Firefox profile and see whether it launches normally there.

I do not know how to do any of this, especially since I cannot open Firefox. Please advise.

Thank you.

macOS Tahoe 26.6（Intel Mac）でFirefoxが使用不能になっています。

【症状】 設定画面や一部のaboutページ（about:networkingなど）は開く 新しいタブを開くと非常に遅い、または開かない アドレスバーで検索してもグルグルのままで結果が出ない about:support は表示されない about:config も開けなくなった アドレスバーにURLを入力してEnterすると消えてしまう

【試したこと】 トラブルシューティングモード → 改善せず 新規プロファイル作成・別プロセス起動 → 同じ症状 完全アンインストール（AppCleaner使用）＋再インストール → 改善せず ベータ版（158.0b1）・安定版（156.0.1）・Nightly すべてで同じ症状 about:config で以下を変更 → 改善せず network.http.http3.enable = false network.dns.native_https_query = false network.dns.disableIPv6 = true

DNS over HTTPS オフ プロキシ設定を「なし」に変更 ハードウェアアクセラレーション関連の変更 ユーザーライブラリ内のFirefox関連フォルダをすべて削除して再インストール

【ターミナルでのエラー（重要）】 textFailed to launch tab subprocess @MachCheckInListener TimedOut Failed to launch gpu subprocess @MachCheckInListener TimedOut Failed to launch socket subprocess @MachCheckInListener TimedOut Failed to launch utility subprocess 完全再インストール後も同じエラーが再現します。

【環境】 macOS: Tahoe 26.6 CPU: Intel Safari: 正常に動作

プロファイルや拡張機能の問題ではなく、子プロセス（content process）の起動自体が失敗している状態です。 ご確認よろしくお願いいたします。

I need help with MacOS Sequoia 15.8.1 (24H32).

Since yesterday’s update to 15.8, Firefox and Thunderbird no longer work—regardless of the build or version. The system immediately terminates the apps with this message in the Apple error report:

System Integrity Protection: enabled Crashed Thread: 0 MainThread Dispatch queue: com.apple.main-thread Exception Type: EXC_GUARD (SIGKILL) Exception Codes: GUARD_TYPE_MACH_PORT Exception Codes: 0x0000000000000203, 0x0000000000000000 Termination Reason: Namespace GUARD, Code 2305843146652647939

Translated with DeepL.com (free version)

Anyone succeed with running Firefox in headless mode under Ubuntu?

I tried:

firefox --headless --safe-mode -P headless https://quan.hoabinh.vn

but got this error:

[12545] Sandbox: CanCreateUserNamespace() unshare(CLONE_NEWPID): EPERM

• • • You are running in headless mode.

[GFX1-]: RenderCompositorSWGL failed mapping default framebuffer, no dt

I installed Firefox as from "https://packages.mozilla.org/apt" repo.

Overnight firefox doesn't launch anymore.

I have firefox installed via Software Manager flatpak (official Mozilla version) but it doesn't launch anymore. Clicking launch does nothing. Version is 156.0

I tried to launch the program in safe mode via console but it straight up doesn't find it?

I would love to add troubleshooting info but I can't actually get to it. I assume an update broke something but no idea how to solve this, can I go to an earlier version?

I updated my Mac to macOS Golden Gate. Tried to update Firefox from a non-admin account. It failed. Went to admin account, deleted Firefox and reinstalled from a new dmg download. All fine in the admin account. But the non-admin account (where I work day to day) won't even launch a Firefox window. It asks for admin access to install a helper. I can't see why it needs this but have given it via username and password, but it still doesn't launch. The dock icon says "Running in Background" when I hover over Firefox and the icon bounces. But no browser window

t takes 4 or more time to open Firefox browser. Each time I get a message that said Firefox is not responding and this locks up the programs. I reboot the systems each time and this does not help to open Firefox browser. What is causing this malfunction and how to fix it?

Firefox on Windows 11. When I try to open Firefox I get a message that Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window. Close does nothing, Task manager - end process does not close. Stuck in a permanent loop here. Rhonda

Kept getting messages that Firefox is unresponsive during use. Has now stopped all together. Uninstalled and reloaded, got a welcome to Firefox message then it went unresponsive again. Now a double click on the App to start does nothing.