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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →The best Firefox extensions for web developers are the ones that fill a specific gap in Firefox’s built-in DevTools. Start with React Developer Tools for React component inspection, Measure-it for quick pixel checks, ColorZilla for sampling colors, Cookie-Editor for targeted cookie debugging, Wappalyzer for an initial technology check, and axe DevTools for accessibility audits. You do not need all of them: choose by task, check the current listing and permissions, and keep Firefox’s native tools for the rest.
Check what Firefox already provides
Firefox’s built-in developer toolkit covers much of everyday development: Inspector, Console, JavaScript Debugger, Network Monitor, Storage panel, Responsive Design Mode, visual editing, Performance and Memory tools, and Style Editor. These are listed on the Firefox Developer Edition page. Developer Edition also has edition-specific features and profile separation; do not assume every detail on that page is exclusive to Developer Edition or absent from standard Firefox.
Use an add-on when it makes a repeated task materially more convenient—for example, inspecting React’s component tree, measuring an element visually, or editing a cookie for a quick test. For layout, network, storage, script, and performance investigations, try the native panel first. That keeps your setup smaller and makes it easier to spot which extension is responsible if a workflow changes.
Best Firefox extensions by development task
The table is a task-based shortlist, not a hands-on ranking. The descriptions below reflect Mozilla Add-ons and Mozilla’s curated developer collection; listings, user counts, permissions, and compatibility can change. Check the current listing before installing.
Recommended Free Tools
#1 Best Overall
| Extension | Useful for | What the listing supports | Fit and limitation |
|---|---|---|---|
| React Developer Tools | React component inspection | Inspect the component hierarchy, props, and state in the Components or Profiler tabs in Firefox DevTools. | The clearest framework-specific pick in this shortlist; useful when ordinary DOM inspection is not enough. |
| Measure-it | Quick pixel measurements | Draw a ruler over a webpage to check width, height, or alignment in pixels. | Useful for a quick visual check, not a replacement for responsive-layout testing. |
| ColorZilla | Sampling page colors | Eyedropper, color picker, gradient generator, and related color tools. | A convenient way to examine colors; not a full design or accessibility audit. |
| Cookie-Editor | Cookie debugging | Create, edit, and delete cookies for the current tab, including for development and quick testing. | Keep changes targeted, especially when the tab has a live authenticated session. |
| Wappalyzer | Technology reconnaissance | Identify technologies used on websites. | Treat results as an initial clue, not definitive proof of a site’s architecture. |
| axe DevTools | Accessibility auditing | Mozilla’s Web Developer’s Toolbox collection describes it as adding accessibility auditing to Firefox Developer Tools. | Automated findings are useful audit input, not proof that an entire site is accessible. |
| Web Developer | General developer controls | The listing broadly describes it as adding various web developer tools to the browser. | The description is broad; check its current listing for the specific feature you need rather than assuming a particular control is included. |
| Stylebot | Temporary appearance tweaks | The Web Development category describes it as a way to change the web’s appearance. | An optional aid for visual adjustments, rather than an essential development extension. |
Inspect React components: React Developer Tools
Choose this when you need to follow a React component hierarchy or inspect component props and state rather than infer everything from rendered markup. Its Firefox DevTools integration provides Components and Profiler tabs. The listing does not establish that it will solve every framework or debugging problem, so pair it with Firefox’s Inspector, Console, and JavaScript Debugger as needed.
Measure a rendered element: Measure-it
Measure-it is for a fast measurement over the page: check a visible element’s width, height, or alignment in pixels with a ruler overlay. It answers “how large is this here?” but not whether the page behaves correctly at other viewport sizes, when content changes, or with keyboard and assistive technology. Use Responsive Design Mode for viewport behavior and treat the ruler as a spot check.
Sample a color: ColorZilla
ColorZilla’s listing describes an eyedropper, color picker, gradient generator, and related tools. It can help identify a color already rendered on a page or work with a color while adjusting a design. Sampling a color does not assess contrast or establish whether a color choice is accessible; check those questions separately.
Rank #2
Test cookies: Cookie-Editor
Use Cookie-Editor when a development task calls for creating, editing, or deleting cookies in the current tab. This can help reproduce a state or check cookie-dependent behavior without turning a general storage investigation into a manual exercise. Be cautious on production sites: editing or deleting cookies can change a logged-in session or other live state. For broader storage debugging, Firefox’s Storage panel remains the native option.
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Identify a site’s technologies: Wappalyzer
Wappalyzer can provide an initial indication of technologies detected on a website. Use it for reconnaissance or to form a hypothesis, then verify important conclusions from the site’s observable behavior or other evidence. A detected technology is not a complete inventory of the site’s architecture, and the listing does not establish that every identification is definitive.
Audit accessibility: axe DevTools
Mozilla’s Web Developer’s Toolbox collection describes axe DevTools as adding accessibility auditing to Firefox Developer Tools. Automated findings can reveal issues worth investigating, but an automated audit alone cannot prove that a whole site is accessible. Treat results as one part of an audit, not as a pass certificate.
General controls and visual overrides
Web Developer may suit someone looking for a broad collection of browser-side developer tools, but Mozilla’s category description is not specific enough to promise a particular feature. Confirm the current listing before choosing it for a concrete workflow. Stylebot is a lower-priority option when you want temporary appearance changes; for changes to the site’s actual source or durable design tokens, use your normal development workflow instead.
How to choose without installing too much
- Name the recurring task. Write down what is inconvenient: following React components, measuring a rendered element, sampling a color, changing a cookie, identifying likely technologies, or collecting accessibility findings.
- Check native-tool overlap. Firefox already includes inspection, debugging, network, storage, responsive, performance, memory, and style tools. Prefer an extension when it offers a clear convenience or task-specific view.
- Read the current Mozilla Add-ons listing. Confirm the extension’s name and developer, description, requested permissions, recent maintenance information, and support for your Firefox version. This shortlist does not verify current compatibility or maintenance for every candidate.
- Install only what the task needs. Add one extension at a time, try it on a development page, and keep it only if it improves the job without disrupting your workflow. The shortlist is not a comparative performance test.
- Recheck when the job changes. Remove tools you no longer use and revisit permissions and compatibility when Firefox or the extension updates.
What Mozilla’s Recommended badge means
Mozilla says Recommended extensions undergo technical review by security experts, followed by automated checks, monitoring, and periodic reviews; Mozilla also says it does not sell Recommended placement. Its guidance is deliberately nuanced: extensions can expose or compromise sensitive data, but the absence of a Recommended badge alone does not establish that an extension is unsafe. Read Mozilla’s Recommended Extensions program, displayed as last updated July 6, 2026.
Use the badge as one signal, not a substitute for checking who publishes the add-on and whether its permissions make sense for the task. Mozilla’s category and collection pages help with discovery; they do not establish comparative performance, security for your particular setup, or compatibility with every Firefox version.
What user counts can—and cannot—tell you
When accessed in 2026, Mozilla Add-ons showed 162,961 users for React Developer Tools, 131,912 for Cookie-Editor, 130,532 for ColorZilla, 116,299 for Wappalyzer, 65,269 for Web Developer, and 20,589 for Measure-it. These are live directory snapshots, not durable market-share figures or evidence of accuracy, security, quality, or fit. They can change, so they are not a sound basis for ranking the extensions.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When an extension is the wrong tool for screenshots
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One GET request can return a PNG, JPEG, WebP, or PDF. See the ScreenshotNeo documentation for the API details and options. These examples use the supplied API base and the Stripe URL; replace the URL and API key for your use case.
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open("shot.webp", "wb").write(r.content)Node.js
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);ScreenshotNeo offers full-page capture with lazy images loaded, CSS-selector element capture, dark mode, 12 device presets and custom viewports, retina scale, PDF paper size/margins/landscape/page ranges, HTML/CSS-to-image, custom CSS and JavaScript, click-before-capture, hide selectors, selector/delay/network-idle waits, request and resource blocking, custom headers, cookies, user agent and Authorization, timezone and geolocation, transparent background, image resizing, configurable-TTL caching, signed links for public image tags, async jobs with signed webhooks, bulk capture of 100 URLs per call, a usage API, and an OpenAPI spec. Other screenshot APIs’ parameter names also work, which can make switching easier.
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Troubleshooting extension choices
- The expected panel or feature is missing: Recheck that you installed the intended extension and read its current listing for the described Firefox integration or feature. For React Developer Tools, look for the Components or Profiler tabs in Firefox DevTools; do not assume another add-on uses the same panel.
- An extension requests permissions that seem unrelated: Pause installation and compare the requested access with its stated job. If the reason remains unclear, do not add it just to test a minor convenience.
- A tool does not work on your Firefox version: Check the current Mozilla Add-ons compatibility information and maintenance details. Compatibility was not verified across versions for every candidate in this article.
- Cookie testing unexpectedly changes a live session: Stop editing that site’s cookies and restore the intended test state through your normal sign-in or development setup. Avoid treating a production session as a safe sandbox.
- A technology result seems conclusive: Treat it as a lead from Wappalyzer, not proof. Verify the specific framework or service before basing an implementation decision on it.
- An accessibility scan reports no issue: Do not interpret that as proof of site-wide accessibility. Automated findings are only one input to a broader audit.
Sources and scope
Mozilla Add-ons listings and category information can change after this article’s research date of September 29, 2026. The recommendations summarize listing descriptions and Mozilla guidance; they are not claims of hands-on testing, independent benchmarking, or a security audit. Mozilla’s documentation on extending developer tools provides broader context for extension panels; its page includes older API-version notes and is not proof of current compatibility.
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