The JavaScript Debugger enables you to step through JavaScript code and examine or modify its state to help track down bugs.

You can use it to debug code running locally in Firefox or running remotely, for example on an Android device running Firefox for Android. See remote debugging to learn how to connect the debugger to a remote target.

To find your way around the debugger, here's a quick tour of the UI.

How to

To find out what you can do with the debugger, refer to the following how-to guides.

Pause execution

You probably want to pause the execution of your code, in order to see what is going on at various points. There are multiple ways to tell the Debugger how and when to pause:

Control execution

What can you do after execution pauses?

Look at values

You probably want to see the value of variables or expressions, either during execution or when it is paused.

Reference