Settings

Opening Settings

To see the Developer Tools Settings pane, open any of the Developer Tools, and then:

either click the "Settings" button () in the Toolbox toolbar:
or press F1 (new in Firefox 43) to toggle between the active tool and the Settings pane
or press Ctrl/Cmd+Shift+O to toggle between the active tool and the Settings pane

The Settings pane looks something like this:

Depicts the Toolbox options

Categories

Default Firefox Developer Tools

This group of checkboxes determines which tools are enabled in the toolbox. New tools are often included in Firefox but not enabled by default.

Available Toolbox Buttons

This group of checkboxes determines which tools get an icon in the Toolbox's toolbar.

Choose DevTools theme

This enables you to choose one of three different themes.

There's a light theme, which is the default:

Light theme for DevTools

A dark theme (the default on Firefox Developer Edition):

Dark theme for DevTools

New in Firefox 48

There's also a Firebug theme that looks like the Firebug extension, letting you feel at home if you're used to Firebug:

Firebug theme for DevTools

Common preferences

Settings that apply to more than one tool. There's just one of these:

Enable persistent logs: A setting to control whether or not the Web Console and Network Monitor clear their output when you navigate to a new page.

Inspector

Show browser styles

A setting to control whether styles applied by the browser (user-agent styles) should be displayed in the Inspector's Rules view. Note that this setting is independent of the "Browser styles" checkbox in the Inspector's Computed view.

Truncate DOM attributes (new in Firefox 47)

By default, the Inspector truncates DOM attributes that are more than 120 characters long. Uncheck this box to prevent this behavior. This setting works by toggling the about:config preference "devtools.markup.collapseAttributes". To change the threshold at which attributes are truncated, you can edit the about:config preference "devtools.markup.collapseAttributeLength".

Default color unit

A setting to control how colors are represented in the inspector:

Hex
HSL(A)
RGB(A)
color name
As authored (new in Firefox 44).

Web Console

Enable timestamps: Controls whether the Web Console displays timestamps. The Web Console defaults to hiding timestamps.

Style Editor

Show original sources: When a CSS preprocessor supporting source maps is used, this enables the Style Editor to display the original, preprocessor, sources rather than the generated CSS. Learn more about Style Editor support for CSS source maps. With this setting checked, the Page Inspector Rules view will also provide links to the original sources.
Autocomplete CSS: Enable the Style Editor to offer autocomplete suggestions.

JavaScript Profiler

Show Gecko platform data: A setting to control whether or not profiles should include Gecko platform symbols.

Editor Preferences

Preferences for the CodeMirror source editor, which is included in Firefox and used by several developer tools, including Scratchpad and the Style Editor.

Detect indentation

Auto-indent new lines based on the current indentation.

Autoclose brackets

Indent using spaces

Tab size

Keybindings

Choose the default CodeMirror keybindings, or keybindings from one of several popular editors:

Vim
Emacs
Sublime Text

Advanced settings

Disable HTTP Cache: Disable the browser HTTP cache to simulate first-load performance in all tabs that have the Toolbox open. This setting persists, meaning that if it is set, caching will be disabled whenever you reopen the devtools. Caching is re-enabled when the devtools are closed. Note that service workers are not affected by this option.
Note that this option was called "Disable Cache" in Firefox versions previous to 49, but it was renamed to make it clearer that this affects the HTTP cache, and not Service Workers/the Cache API.
Disable JavaScript: Reload the current tab with JavaScript disabled.
Enable Service Workers over HTTP: Enable Service Worker registrations from insecure websites.
Enable browser chrome and add-on debugging toolboxes: Enable you to use developer tools in the context of the browser itself, and not only web content.
Enable remote debugging: Enable the developer tools to debug remote Firefox instances.