There's also a Firebug theme that looks like the Firebug extension, letting you feel at home if you're used to Firebug:
Preferências comuns
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.
Inspetor
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
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.
Enable layout panel
Enable the experimental layout panel. This setting only exists in Firefox Nightly.
Consola da Web
Enable timestamps
Controls whether the Web Console displays timestamps. The Web Console defaults to hiding timestamps.
Enable new console frontend
Switch to the experimental new console. This setting only exists in Firefox Nightly.
Enable the Style Editor to offer autocomplete suggestions.
Comportamento da Captura de Ecrã
Screenshot to clipboard
When you click the icon for the Screenshot tool, copy the screenshot image to the clipboard (the image will still be saved to your Downloads directory). New in Firefox 53.
Play camera shutter sound
When you click the icon for the Screenshot tool, play a shutter sound. New in Firefox 53.
Preferências do Editor
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
Configurações avançadas
Show Gecko platform data
A setting to control whether or not profiles should include Gecko platform symbols.
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 a panel within the debugger to debug workers.
Nota: This option got removed from the UI in Firefox 56, because this version ships with a new Debugger UI, but it can still be enabled for the old UI by setting the preference devtools.debugger.workers to true.