Eclipse Debug configuration

Select Run->Open Debug Dialog… from the Eclipse menu
Right-click on C/C++ Local Application and select New
Project: firefox (or select your project name)
C/C++ Application: (select browse and choose mozilla/../obj-i686-pc-linux-gnu/dist/bin/firefox-bin)

Specific configuration

1. In the Arguments tab, change the working directory to mozilla/../obj-i686-pc-linux-gnu/dist/bin/
2. In the Environment tab, create two variables,

 Name:  LD_LIBRARY_PATH
 Value: .:./plugins:.

 Name:  LIBRARY_PATH
 Value: .:./components:.

3. In the Debugger tab, remove the checkbox on "Stop on startup at:"
4. Click Apply and hit Debug to start debugging Firefox

Troubleshooting & Known Issues

MUST-READ

If you get a GDB timeout error when debugging, open the debug configuration (Run->Open Debug Dialog...->firefox) and remove any entry in the Sources tab. (I had this problem after adding my mozilla folder to a svn repository). GDB tries to "cache" every mozilla subfolder (without exclusion). The complete fix is available from the Documentation. ALSO, this workaround increases the the debug launch speed to the point that you won't have to wait to start debugging.

CategoryMozillaTeam