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Firefox Developer ToolsVisBug
Free

Free and included with Firefox.

 Free

The open-source extension is available without a license fee.

Windows, macOS, Linux Web, Browser extension
  • Built into Firefox with nothing extra to install
  • Can debug Firefox for Android remotely
  • Edit spacing, type and colour on a live page without touching developer tools
  • Measurement and accessibility inspection built into the same toolbar
  • Only available inside Firefox
  • Tests Firefox's engine, so other browsers still need their own tools
  • Changes are temporary and vanish on reload
  • Complex layouts can behave unpredictably when dragged
Downloadable app Browser extension
Open source Open source
License: MPL-2.0 License: Apache-2.0
No account needed Not stated if an account is needed
Works offline Not stated if it works offline

Checked September 23, 2026

Checked September 22, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.