Debugging

Debugging a project as large as Mozilla can be a daunting task. Fortunately, over the years, Mozilla developers have come up with not just technologies and features to help you debug code, but have devised tips and techniques that can help too. Also available are assorted tools that you can use when debugging.

Documentation topics

Debugging on top of the Mozilla platform

Debugging JavaScript code: How to debug JavaScript code, with a focus on debugging code in the Mozilla project itself.
Debugging a XULRunner application: Tips and suggestions that will help you debug your XULRunner based application.
Debugging on Boot to Gecko: Debugging Firefox OS (apps and the platform itself)
Debugging update problems: Learn how to debug update problems in Mozilla-based applications.

Debugging the Mozilla platform

Using debuggers with Mozilla

Debugging Mozilla on Windows FAQ: Questions (and answers) about debugging Mozilla on Windows.
Debugging Mozilla on OS X: Questions (and answers) about debugging Mozilla on OS X.
Debugging Mozilla with gdb: gdb is our primary debugger on Mac and Linux.
Debugging Mozilla with lldb: lldb is the new debugger on Mac.

Advanced debugging techniques

Understanding crash reports: How to read crash reports, which are full of information yet often not easy to interpret and act on.
Debugging a minidump: Windows crash reports include a minidump, which contains a lot of information about the application when it crashed.
Debugging Mozilla with valgrind: Valgrind is a memory debugger for Mac and Linux. It is slow, but good for tracking down difficult memory safety bugs.
Replay debugging Firefox with VMWare Workstation: How to setup record and replay debugging on Firefox, to help debug intermittent mochitest failures.
Detecting defects in Firefox with Coverity: Coverity is a static analysis system that can detect defects in Firefox.
Gecko Logging: Using old-school logging to try to track down what's going on.

Debugging specific parts of the Mozilla codebase

Debugging OpenGL: If you're working on code that involves OpenGL calls, and need to debug it, you can turn on a special OpenGL debugging mode.
Debugging frame reflow and Debugging table reflow: Notes on debugging issues in Gecko's layout engine.

Miscellaneous

Debugging Safari: Some tips for debugging Safari
Debugging Chrome: Some tips for debugging Chrome
Debugging Internet Explorer: Some tips for debugging Internet Explorer

Providing useful information to the Mozilla developers

How to get a stacktrace for a bug report: Useful information you can provide about a crash.
Reporting a Performance Problem: ...using the Gecko Profiler extension.
Debugging a hang on OS X: Collecting "samples" to attach to a bug.
Remote debugging: Core dumps and examples of remote debugging. Useful if a developer can't reproduce your crash.
HTTP logging: How to log HTTP network traffic for debugging purposes.

Debugging tools

Tools: Assorted tools that will help you debug your code or web site.
nserror lookup: Useful for when your code gets a complicated numeric error code and you can't figure out what it means.
Download a debug build: Recent automatically compiled debug builds are available. Note that these are replaced frequently by our tinderboxes. The debug builds have "-debug" at the end of their file names.