Browser Toolbox

The Browser Toolbox enables you to debug add-ons and the browser's own JavaScript code rather than just web pages like the normal Toolbox.  The Browser Toolbox's context is the whole browser rather than just single page on a single tab.

Note:  If you want to debug a specific add-on that is restartless or SDK-based then try the Add-on Debugger.  Use the Browser Toolbox for add-ons that are neither.

Enabling the Browser Toolbox 

The Browser Toolbox is not enabled by default.  To enable it you need to check the settings "Enable chrome and addon debugging" and "Enable remote debugging".

To do this, open the Developer Tools Toolbox's Settings, go to the section "Advanced Settings", and check the settings "Enable chrome and addon debugging" and "Enable remote debugging".

Opening the Browser Toolbox

Open the Browser Toolbox through the menu button new fx menu and the menu items "Developer" then "Browser Toolbox". 

Click the menu item and you'll be presented with a dialog like this (this can be removed by setting the devtools.debugger.prompt-connection property to false):

Click OK, and the Browser Toolbox will open in its own window:

You'll see, and be able to debug, all the JavaScript files loaded by the browser itself and by any add-ons that are running. Altogether you will have access to the following developer tools:

Debugging chrome: and about: pages

From Firefox 37 onwards, you can debug chrome: and about: pages using the normal Debugger, just as if they were ordinary content pages.