Crash log file created by Google BreakPad, an open source crash reporting tool used by products such as Mozilla Firefox; may be saved to the local file system upon program crash; can be submitted to the software developers to determine the cause of the crash.
EXTRA files created by Mozilla Firefox are saved to the [user]\AppData\Roaming\Mozilla\Firefox\Crash Reports\pending\ directory.
NOTE: EXTRA files are often accompanied by .DUMP files as well.