Lighthouse is Google's open-source web auditing tool. It's built into Chrome DevTools — but where does Firefox fit in? Firefox doesn't ship Lighthouse natively, but you can still run Lighthouse against Firefox-served pages and use Firefox's own overlapping tools. This guide covers how to use Lighthouse from Firefox, what Firefox's native tools cover, and where the gaps are.
Running Lighthouse on Firefox-Served Pages
Lighthouse itself is a Node.js tool. You don't need Chrome to run it — you can run it against a URL from the command line:
npm install -g lighthouse
lighthouse https://example.com --output html --output-path report.html
This runs Lighthouse using Chromium (headless) but audits any URL, including your Firefox-tested app. The results are the same whether you access it from Firefox or Chrome — they measure the page itself.
Open the report.html in Firefox to read results. This is the fastest path.
Lighthouse CLI for CI/CD
For automated auditing in pipelines:
# Install
npm install -g lighthouse
# Run with JSON output for parsing
lighthouse https://example.com --output json --output-path report.json --chrome-flags="--headless"
# Parse scores
node -e "
const r = require('./report.json');
console.log('Performance:', r.categories.performance.score * 100);
console.log('Accessibility:', r.categories.accessibility.score * 100);
console.log('Best Practices:', r.categories['best-practices'].score * 100);
console.log('SEO:', r.categories.seo.score * 100);
"
This gives you the same Lighthouse scores as Chrome DevTools, without opening Chrome.
Firefox's Built-In Alternatives
Firefox doesn't have Lighthouse, but its DevTools cover much of the same ground natively:
Performance (vs. Lighthouse Performance)
DevTools → Performance panel: records a timeline profile with JS execution, layout, paint, and composite. Shows Main Thread activity and Frame Rate.
For Core Web Vitals:
- LCP (Largest Contentful Paint): visible in the Performance panel's "paint" events
- CLS (Cumulative Layout Shift): watch the "Layout" track for unexpected reflows
- FID/INP: measure event handler responsiveness in the Timeline
Firefox's profiler is more detailed than Lighthouse's performance audit — it shows call trees and identifies specific JS functions causing slowness, which Lighthouse doesn't.
Accessibility (vs. Lighthouse Accessibility)
DevTools → Inspector → Accessibility panel covers:
- ARIA roles and names
- Keyboard tab order (Show Tabbing Order)
- Color contrast ratios
- Check for issues button (automated scan)
Firefox's built-in accessibility checking is comparable to Lighthouse's accessibility audit and catches many of the same issues (missing alt text, low contrast, missing form labels).
Network (vs. Lighthouse Best Practices / Performance)
DevTools → Network panel shows:
- Total request count and sizes
- Whether resources are compressed
- Cache headers
- HTTP/2 vs HTTP/1.1 usage
- Which resources are render-blocking
Manually review the list against Lighthouse best-practice recommendations.
Console (vs. Lighthouse Best Practices)
Firefox's Console flags issues that Lighthouse's Best Practices audit catches:
- Mixed content warnings
- Deprecated API usage
- CSP violations
- HTTP error responses
PageSpeed Insights (Firefox-Accessible Alternative)
Google's PageSpeed Insights (web tool) runs Lighthouse against your URL from Google's servers and shows results in a browser. Works fine from Firefox. Useful because it tests from a neutral server location, not your local machine.
Access it directly in your Firefox browser at the PageSpeed Insights URL. Results include field data from Chrome User Experience Report (CrUX) as well as lab data.
webpagetest.org in Firefox
WebPageTest.org is more powerful than Lighthouse for performance testing:
- Tests from multiple real locations worldwide
- Tests on real mobile devices
- Shows Filmstrip View (visual loading progression)
- Waterfall charts more detailed than Lighthouse
- Can test with Firefox as the test browser (select in settings)
Access the WebPageTest site from Firefox — it's a full web app.
axe DevTools Extension for Firefox
axe DevTools (available on Firefox Add-ons) is the engine behind Lighthouse's accessibility audit, available as a Firefox extension:
- Install axe DevTools from AMO
- Open DevTools (F12)
- Navigate to the "axe DevTools" panel
- Click "Scan" — identical methodology to Lighthouse accessibility audit
This gives you Lighthouse-equivalent accessibility scores without leaving Firefox.
Comparing Scores: Firefox Tools vs. Lighthouse
| Audit Category | Lighthouse | Firefox Native Tools |
|---|---|---|
| Performance | ✅ Score + recommendations | ✅ Profiler (more detail, no score) |
| Accessibility | ✅ Score + list | ✅ Inspector + axe extension (comparable) |
| Best Practices | ✅ Automated | ⚠️ Manual network/console review |
| SEO | ✅ Automated | ⚠️ Manual (check meta tags, headings) |
| PWA | ✅ Automated | ❌ No equivalent |
Bottom line: for a scored Lighthouse report, run it from the CLI or use PageSpeed Insights from Firefox. For detailed debugging, Firefox's tools are often more useful than Lighthouse's summary.
When to Use Each
- Lighthouse: getting a score for stakeholder reporting, quick check of all categories at once, CI/CD pass/fail gate
- Firefox DevTools: deep-dive debugging of specific issues, accessibility inspection, CSS debugging, JavaScript profiling
- WebPageTest: understanding real-world performance from different locations
- PageSpeed Insights: field data from real users (CrUX)
Using them together gives the most complete picture — Lighthouse for the summary, Firefox DevTools for the investigation.
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