Quick wins for a faster PC:
Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →The best Firefox extensions for web developers are the ones that fill a specific gap in Firefox DevTools. Start with Firefox’s Inspector, Console, JavaScript Debugger, Network Monitor, Storage panel, Responsive Design Mode, Performance and Memory tools, and Style Editor. Then add an extension for a recurring task such as React component inspection, pixel measurement, cookie editing, technology identification, or accessibility auditing.
This shortlist uses current Mozilla Add-ons listings and Mozilla support pages accessed in 2026. Listings, permissions, compatibility and user counts can change, so open the current add-on page before installing.
Choose by the job you need to do
There is no universal “best” developer extension. Match the add-on to a concrete workflow, check whether Firefox already handles it, and remove extensions you no longer need. The table below summarizes the strongest task matches in Mozilla’s current Web Development category and related curated collection.
| Job | Extension | What the listing says it does | Important qualification |
|---|---|---|---|
| Inspect React applications | React Developer Tools | Inspect a React tree, including component hierarchy, props and state, in Components or Profiler tabs in Firefox DevTools. | Useful for React-specific inspection; it does not replace the general Inspector, Console or Debugger. |
| General web-development controls | Web Developer | Adds various web developer tools to the browser. | Mozilla’s broad listing does not establish every individual feature, so verify the current description before relying on a particular control. |
| Measure pixels quickly | Measure-it | Draws a ruler over a page to check element width, height or alignment in pixels. | A visual spot check, not a substitute for responsive-layout testing at multiple viewports. |
| Sample colors | ColorZilla | Provides an eyedropper, color picker, gradient generator and related color tools. | Convenient for examining colors; it is not a complete contrast or accessibility audit. |
| Edit cookies | Cookie-Editor | Create, edit and delete cookies for the current tab for development and quick testing. | Use carefully on authenticated production sessions. |
| Identify a site’s technologies | Wappalyzer | Identifies technologies used on websites. | Treat results as an initial clue, not definitive proof of the site’s complete architecture. |
| Run accessibility checks | axe DevTools | Adds accessibility auditing to Firefox Developer Tools, according to Mozilla’s Web Developer’s Toolbox collection. | Automated findings are audit input; passing the scan does not prove that an entire site is accessible. |
| Make temporary visual changes | Stylebot | Changes a website’s appearance. | Optional for quick visual experiments, not an essential debugging tool. |
Mozilla’s category snapshot 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 when accessed in 2026. These are live directory counts, not market-share, quality or security measurements; do not rank extensions by them.
PC Slower Than It Used to Be?
A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Crashes, No Sound, or Screen Glitches?
Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minute#1 Best Overall
Firefox’s built-in tools come first
Firefox Developer Edition lists the Inspector, Console, JavaScript Debugger, Network Monitor, Storage panel, Responsive Design Mode, visual editing, Performance and Memory tools, and Style Editor. Standard Firefox also includes a substantial developer toolbox, although Developer Edition has edition-specific features and profile separation that should be checked against Mozilla’s current documentation.
Use an extension when it makes a specialized task faster or adds framework-aware information. For example, React Developer Tools exposes component hierarchy, props and state in a way the generic DOM Inspector cannot. Conversely, opening the Inspector is usually preferable to installing an extension merely to inspect HTML and CSS.
Best extensions by workflow
React Developer Tools for component debugging
Install React Developer Tools when you routinely need to inspect component boundaries, props, state or profiling information. After installation, open Firefox DevTools and look for the Components or Profiler tabs described by the AMO listing. If the tabs do not appear, confirm that the page is a React application, reload it, and check the extension’s current compatibility notes.
Keep the distinction between development and production in mind: a tool that recognizes a React tree cannot reveal components that are not present in the loaded page, and it does not replace network, console or performance investigation.
Rank #2
- HTML CSS Design and Build Web Sites
- Comes with secure packaging
- It can be a gift option
Measure-it for a fast visual ruler
Measure-it is appropriate when a designer or developer asks, “How many pixels wide is this gap?” Draw the ruler over the page, record the dimensions, then verify the result in Inspector and Responsive Design Mode. Overlays measure what is rendered at one viewport; they do not tell you whether a layout remains correct at other widths, zoom levels or device pixel ratios.
ColorZilla for sampling and palette work
ColorZilla’s eyedropper and color-picker tools shorten the path from a rendered color to a CSS value. Use it to investigate a brand color, gradient or suspicious visual difference, then validate the value in your stylesheet and run a proper contrast and keyboard-accessibility review. A sampled color alone says nothing about whether text meets accessibility requirements.
Cookie-Editor for targeted state testing
Cookie-Editor is useful for reproducing cookie-dependent states: consent choices, feature flags, locale selectors or an authentication edge case. Work in a test profile or staging environment where possible. Before changing a live tab, note that deleting or altering session cookies can sign you out or change server-side behavior. Clear only the cookie relevant to the test and restore the original state afterward.
Wappalyzer for initial technology reconnaissance
Wappalyzer can provide a quick indication of frameworks, analytics, hosting or other technologies exposed by a site. Use the result to decide what to inspect next, not as evidence that you know the full stack. Server-side components, custom builds and hidden services may not be detectable from the browser.
Recommended Free Tools
Rank #3
axe DevTools for accessibility audit input
Mozilla’s Web Developer’s Toolbox collection describes axe DevTools as adding accessibility auditing to Firefox Developer Tools. Run it after a feature is rendered and treat each result as a lead to verify manually. Check keyboard navigation, focus order, accessible names, zoom, reduced motion and real content; automated rules cannot cover every usability or assistive-technology issue.
Web Developer for a broad utility set
The Web Developer listing says it adds various web developer tools, making it a candidate when you want a consolidated utility toolbar. Because the listing’s description is broad, inspect the current add-on page and permissions before depending on a specific command. Firefox’s native panels may already cover the operation you need with fewer moving parts.
Stylebot for temporary appearance experiments
Stylebot is a lower-priority option for trying visual adjustments without editing the source repository. Use it to test a hypothesis—such as spacing, color or typography—then make the real change in your codebase and test across browsers. Treat browser-only styling as a local experiment, not a production fix.
How to evaluate an extension before installing
- Confirm the identity. Open the Mozilla Add-ons listing, check the exact name and developer, and avoid similarly named copies.
- Define the job. Write down the recurring task the extension must solve. If you cannot name one, do not install it.
- Compare native coverage. Try Inspector, Console, Network, Storage or Responsive Design Mode first.
- Read permissions. Requested access should be proportionate to the task. A cookie editor necessarily needs powerful page or storage access; a simple ruler should not need unrelated privileges.
- Check maintenance and compatibility. Review the current listing’s last-update information, supported Firefox versions and issue or support details.
- Prefer review signals without treating them as guarantees. Mozilla says Recommended extensions receive technical review by security experts, automated checks, monitoring and periodic reviews. Mozilla also says it does not sell Recommended placement. The absence of a Recommended badge alone does not prove an extension is unsafe.
- Install the minimum. Fewer extensions reduce permission exposure, UI clutter and possible conflicts. Remove tools that no longer earn their place.
Mozilla’s guidance is deliberately nuanced: many add-ons are built honestly, but extensions can expose or compromise sensitive data. Read the listing and permissions yourself rather than assuming a badge or user count settles the question.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsRank #4
- Brand: Wiley
- Set of 2 Volumes
- A handy two-book set that uniquely combines related technologies Highly visual format and accessible language makes these books highly effective learning tools Perfect for beginning web designers and front-end developers
A practical Firefox developer setup
- Keep the built-in DevTools panels visible that match your work: Inspector, Console, Network and Storage are a strong baseline.
- Add React Developer Tools only for React projects, or choose the task-specific extension that matches your current problem.
- Create a separate Firefox profile for development and testing so experimental extensions, cookies and site permissions do not contaminate personal browsing.
- Use Responsive Design Mode and real devices or emulators to test breakpoints; use Measure-it only for quick visual measurements.
- Run axe DevTools, then perform manual keyboard and screen-reader checks before calling an accessibility issue resolved.
- Document extension versions and Firefox versions in team troubleshooting notes, because listings and compatibility can change.
Troubleshooting common problems
The extension appears installed but has no effect
Reload the page, confirm the extension is enabled, and check whether the site is a privileged page such as an internal about: URL where extensions may be restricted. For React Developer Tools, verify that the page actually contains a detectable React application.
DevTools panels are missing
Open DevTools again after installation, use its panel overflow menu, and check the extension’s current listing for supported Firefox versions. A browser restart can help after an update.
A cookie change did not alter the application
Verify the cookie’s domain, path, secure flag and expiration, then reload. The application may also store state in local storage, session storage or a server-side session; inspect the Storage panel rather than assuming cookies are the only control.
A technology result looks wrong
Wappalyzer can only infer what the page exposes. Compare its result with response headers, source, Network requests and the site’s public documentation. Do not treat an inferred technology as confirmed architecture.
An accessibility scan reports nothing
Check that the relevant content is rendered, run the scan after dynamic updates, and perform manual tests. No automated result is not the same as no accessibility issue.
The browser becomes slower or pages behave differently
Disable extensions one at a time, reproduce the problem in a clean profile, and inspect permissions and update history. Keep only the extension that solves a demonstrated need.
Capture a clean reproduction without browser setup
When a bug report needs a rendered page image, ScreenshotNeo is the first service to try: it accepts consent banners before capture, removes more than 60 known consent platforms plus newsletter popups and chat widgets, and bills only clean shots. Bot checks, blank pages, timeouts, failed loads and cache hits are not billed, with the result identified by response headers.
cURL:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpPython:
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
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}`);See the ScreenshotNeo documentation for options such as full-page capture, CSS selectors, device presets, dark mode, custom JavaScript, waits, cookies, headers, PDF output, caching, signed links, asynchronous jobs and bulk capture. Its MCP server provides take_screenshot, get_page_info and capture_pdf tools for Claude, Cursor and other MCP clients. The Free plan includes 1,000 screenshots per month without a card; paid plans start at $5 for 3,000. Create a free ScreenshotNeo account.
Frequently Asked Questions
Should I install every extension in this list?
No. Start with Firefox DevTools and add only the tool that solves a recurring, clearly defined task.
Are Mozilla Recommended extensions guaranteed safe?
No. Mozilla describes technical review, automated checks and monitoring, but you should still inspect the developer, permissions and current maintenance information.
Do user counts show which extension is best?
No. Add-on counts are changing directory snapshots and do not measure accuracy, security or suitability.
Can Wappalyzer prove a website’s entire technology stack?
No. It provides an initial identification based on what the site exposes; confirm important conclusions with other evidence.
Free tools Windows power users keep installed
One-click scans. No signup required.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
