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Firefox Developer Tools

firefox-source-docs.mozilla.org

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Spec score 8.7 #7 of 30 in Debugging Software

Spec sheet

Purpose
Firefox Developer Tools are built into Firefox and let web developers examine, edit, and debug HTML, CSS, and JavaScript.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Supported platforms
desktopRead 21 Sep 2026 · firefox-source-docs.mozilla.org
Free plan
YesRead 21 Sep 2026 · firefox-source-docs.mozilla.org
Maker
Mozilla says Mozilla Corporation makes Firefox and was established in August 2005 as a wholly owned taxable subsidiary of Mozilla Foundation.Read 12 Oct 2026 · mozilla.org
Accessibility
The Accessibility Inspector exposes the page’s accessibility tree so developers can identify missing information or issues.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Accessibility performance note
When enabled, the accessibility engine runs in the background and may affect other panel metrics and overall browser performance.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Additional tools
Built-in tools include Memory, Storage Inspector, Style Editor, screenshot, rulers, and JavaScript tracing features.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
AI integration
The docs list Firefox DevTools MCP, an MCP server that enables AI assistants to automate and interact with Firefox.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Browser and add-on debugging
The Browser Console displays messages from the browser and add-ons and can run JavaScript in the browser’s scope.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Browser debugging
The Browser Console displays messages from the browser and add-ons and can run JavaScript in the browser’s scope.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Browser engine
geckoRead 21 Sep 2026 · firefox-source-docs.mozilla.org
Configuration
Developer Tools can be docked at the bottom or side of the browser window or opened in a separate window.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Developer audience
Firefox Developer Edition is described as a browser made for developers and includes developer tools in beta.Read 12 Oct 2026 · mozilla.org
Extension support
The documentation describes extending Firefox DevTools through browser extensions.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
JavaScript debugger
The JavaScript Debugger lets users step through code and examine or modify its state to track down bugs.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Limit of network simulation
Responsive Design Mode says its network throttling is approximate and should not be relied on for exact performance measurements.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Network Monitor
The Network Monitor displays HTTP requests, their durations, and request details.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Open source
YesRead 21 Sep 2026 · firefox-source-docs.mozilla.org
Page Inspector
The Page Inspector examines and modifies a page’s HTML and CSS, including its box model, fonts, animations, and layouts.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Remote debugging
DevTools can connect to targets in other browsers or devices, including Firefox for Android.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Responsive testing
Responsive Design Mode simulates device screen sizes, pixel density, touch, and network conditions to test how a site looks and behaves.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Storage
The Storage Inspector can inspect cookies, local storage, IndexedDB, and session storage on a page.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Supported download platforms
Firefox Developer Edition download options listed include Windows, macOS, and Linux builds.Read 12 Oct 2026 · mozilla.org
Web app debugging
The Application panel includes tools for inspecting and debugging progressive web apps, service workers, and web app manifests.Read 12 Oct 2026 · firefox-source-docs.mozilla.org
Web Console
The Web Console logs page-related information and lets users execute JavaScript expressions in the page context.Read 12 Oct 2026 · firefox-source-docs.mozilla.org

Plans and prices

Firefox Developer Tools Free Built into Firefox · examines, edits, and debugs HTML, CSS, and JavaScript Read 12 Oct 2026 · firefox-source-docs.mozilla.org

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