If you file a bug report in Bugzilla about a crash you should include a stacktrace (call stack) in your report. A stacktrace will tell Mozilla developers what crashed and provide a starting point for investigating its cause. This article describes how to use the Mozilla Crash Reporter (Breakpad) to get a crash ID and alternative ways to create a stacktrace.
You need a binary build of Firefox 3 or newer from Mozilla.org. SeaMonkey 2, Thunderbird 3, and Sunbird 1 also support Breakpad, however some steps below will be somewhat different.
Mozilla's crash report server currently only has debug information for Mozilla builds and thus the crash reporter cannot work if you use a build from a Linux distribution or if you compile from source code. In these cases you will need to use one of the alternative methods listed below.
How to get a crash ID with the Mozilla Crash Reporter
The Mozilla Crash Reporter window should automatically come up after Mozilla crashes. If you have any additional information about the crash, such as additional detail on what you were doing at the time that may have triggered the crash, please enter it into the comments box. Be sure that you checked the "Tell Mozilla about the crash" checkbox and click the restart button.
The crash reporter should now submit the crash report and Firefox should open again. To access your submitted reports, type "about:crashes" in the Firefox URL bar and press enter. Firefox should open a list of all your submitted crash report IDs. Copy the IDs of the appropriate crashes to your Bugzilla bug report. Please check the listed times to avoid copying the ID of an unrelated crash report.
How to get the crash ID if Firefox crashes on startup
If Firefox crashes on startup you can still access your submitted crash reports. Crash reports are accessible from all Firefox profiles, so if a new profile does not crash you can use it to access them through "about:crashes" as above.
Accessing crash report IDs outside of Firefox
If you cannot load Firefox at all you can find the crash report files at this location depending on your operating system:
Windows : %APPDATA%\Mozilla\Firefox\Crash Reports\submitted\
Mac OS : ~/Library/Application Support/Firefox/Crash Reports/submitted/
Linux : ~/.mozilla/firefox/Crash Reports/submitted/
Each file in this folder contains one submitted crash report ID. You can check the modified or creation time for each file to discern which crash reports are relevant to your bug report.
Alternative ways to get a stacktrace
If the Mozilla crash reporter doesn't come up or isn't available you will need to obtain a stacktrace manually:
See the article Create a stacktrace with Windbg for information on how to do this.
You can also use WinDbg if you get a hang or freeze instead of a crash. In that case use the command:
!analyze -v -hang
Note that for most distros the package you need to get symbols for will be something like "xulrunner", not "firefox".