Capturing a minidump

Minidumps are files created by various Windows tools which record the complete state of a program as it's running, or as it was at the moment of a crash. Small minidumps are created by the Breakpad crash reporting tool, but sometimes that's not sufficient to diagnose a problem. For example, if the application is hanging (not responding to input, but hasn't crashed) then Breakpad is not triggered, and it can be difficult to determine where the problem lies. Sometimes a more complete form of minidump is needed to see additional details about a crash, in which case manual capture of a minidump is desired.

This page describes how to capture these minidumps on Windows, to permit better debugging.

Privacy and Minidumps

Capturing a Minidump: Application Crash

To capture a full minidump for an application crash, you can use a tool called windbg.

1. Download the Windows Debugging Tools and install the 32-bit version. Even if you are on a 64-bit Windows, your Firefox is likely to be a 32-bit one as of this writing (Firefox 4 era). To double-check, you can open about:support in the browser, and look at the "User Agent" entry. If it includes the string "Win64", then you actually need the 64-bit version. NB: "WOW64" does not indicate a 64-bit browser, but rather a 32-bit browser running on 64-bit Windows; you need the 32-bit tools listed above.
2. Run WinDbg (Start → All Programs → Debugging Tools for Windows → WinDbg), and select File → Open. Choose the Firefox executable, called firefox.exe, and usually found in "C:\Program Files\Mozilla Firefox". (On 64-bit versions of Windows, you may find it in "C:\Program Files (x86)\Mozilla Firefox" instead.)
3. From the menu, select Debug → Go, and Firefox should start. If the debugger spits out some text right away and Firefox doesn't come up, select Debug → Go again.
4. When the program is about to crash, WinDbg will spit out more data, and the prompt at the bottom will change from saying "*BUSY*" to having a number in it. At this point, you should type ".dump /ma c:\firefoxcrash.dmp" -- without the quotes, but don't forget the dot at the beginning. Once it completes, which can take a fair while, you will have a very large file at c:\firefoxcrash.dmp that can be used to help debug your problem.
5. Ask in the relevant bug or thread how best to share this very large file!

Capturing a Minidump: Application Hang

On Windows Vista and Windows 7, you can follow these instructions to capture a dump file and locate it after it's been saved.