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 ToolsSettings, go to the sectionAdvanced Settings, and check the settings “Enable browser chrome and add-on debugging toolboxes” and “Enable remote debugging”.

Opening the Browser Toolbox

Open the Browser Toolbox through the menu button and the menu items “Developer” then “Browser Toolbox”.

You can also open it with theCtrl +Alt +Shift +I key combination (Cmd +Opt +Shift +I on a Mac).

You will be presented with a dialog like this (it can be removed by setting thedevtools.debugger.prompt-connection property to false):

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

You’ll be able to inspect the browser’s chrome windows and 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:

• Debugger

• Console

• Style Editor

• Performance

• Network Monitor

• Page Inspector

• Accessibility Inspector

You can debug chrome: and about: pages using the normalDebugger, just as if they were ordinary content pages.

Targeting a document

In the normal toolbox, there’s abutton in the toolbar enabling you to target specific iframes in the document. The same button appears in the browser toolbox where it lists all the top-level chrome and content windows as well as any iframes they contain. This enables you to inspect documents in individual chrome windows and popups, as well as in content tabs.

For example, here’s what the frame selection popup lists when there are two browser windows open, one with one content tab, and one with two:

Debugging popups

It’s hard to debug popups, because the browser hides them as soon as you click outside them. There is a way to disable this behavior. Click the toolbox menu and selectDisable popup auto-hide.

Now when you open any popup, it will stay open until you press theEsc key. You can use the Inspector’s node picker to select that panel, and examine and modify its content.

You can use the same technique to debugpopups created by add-ons.