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    How to Report a Hung Firefox

    Note: This article is intended for developers and technically-knowledgeable users. If that's not you, or you just want to fix a Firefox hang without reporting it, see Firefox hangs or is not responding - How to fix.

    Is your Firefox not responding? Or are you regularly seeing the "Firefox is running but is not responding..." dialog? This usually means that something in Firefox is hung. This may be because of a code error within Firefox itself, such as a deadlock or infinite loop, or it may be caused by 3rd-party software such as a Firefox extension, antivirus software, or even malware or a virus on your computer.

    The easiest way to help the Firefox stability team to debug these kinds of hangs is to make the hung Firefox crash and submit a crash report. Then file a bug report with the crash report ID. The steps to induce a crash are slightly different on each platform:

    Windows

    On Windows, the stability team has written a utility which will inject a crash into Firefox which will trigger the crash reporter: Download crashfirefox.exe here (source code). Running this tool will search for firefox.exe and inject crashing code into it. The tool also has command-line options to kill processes with other names or by process ID.

    • Run the crashfirefox.exe tool.
    • The Firefox crash report UI should appear. Please check the box to send the crash report to Mozilla
    • Start Firefox. Type "about:crashes" in the URL bar and click on the top listing. The crash report should look something like this report, which is an example of bug 1132241.
    • Create a new bug report at bugzilla.mozilla.org using this link.

    Linux and Mac

    On Mac, these instruction require Firefox 27 or newer. Download Firefox Nightly here.

    On Linux and Mac, sending SIGABRT to a process will trigger the crash reporter. You can use any process monitoring tool to find the Firefox process ID (PID).

    Finding the Firefox PID using a system monitoring tool (Linux screenshot).

    Then, in a terminal, kill Firefox using a command such as this:

    # Replace 31042 with the PID of Firefox found above
    kill -n SIGABRT 31042
    • The Firefox crash report UI should appear. Please check the box to send the crash report to Mozilla
    • Start Firefox. Type "about:crashes" in the URL bar and click on the top listing.
    • Create a new bug report at bugzilla.mozilla.org using this link.

    Other Techniques

    Instead of crashing Firefox, more advanced developers who know how to use a debugger can try attaching to the Firefox process and debugging in place. This is only useful if you have Firefox debug symbols, which are available on Windows from the Mozilla symbol server.

    Document Tags and Contributors

    Contributors to this page: bedwards, John99, ishita, BenjaminSmedberg, jswisher, Aleksej
    Last updated by: Aleksej,