Quick answer
Use link rel=icon with accurate type and sizes metadata. Firefox can select among declared candidates, so each URL should resolve to the format and dimensions it claims.
- Last verified
- July 31, 2026
- Evidence
- Primary documentation plus transparent editorial analysis
- Primary sources
- 2
Declare interoperable icon candidates
Use link rel=icon with accurate type and sizes metadata. Firefox can select among declared candidates, so each URL should resolve to the format and dimensions it claims.
A self-contained SVG with an explicit viewBox is a strong scalable candidate; retain PNG and root ICO fallbacks for other clients and surfaces.
Connected next stepSafari Favicons: Tabs, Pinned Tabs, and Apple Touch Icons for the closest prerequisite or comparison.
Test tabs and saved surfaces separately
A correct current tab does not prove that an older bookmark thumbnail has refreshed. Open every asset URL, inspect the final document head, then compare a fresh private window and an existing profile.
Keep the icon consistent across pages on the same hostname unless route-specific branding is an intentional, tested product requirement.
Connected next stepFavicons in Microsoft Edge: Tabs, Favorites, PWAs, and Cache for the next connected implementation decision.
Separate deployment errors from cache state
First confirm HTTP 200, an image Content-Type, a decodable square file, and the expected bytes. Only after those checks pass should you clear temporary cached files or use a cache-bypassing reload.
Changing the filename during diagnosis can prove that an old response is cached, but stable production filenames and deliberate cache headers are easier to operate long term.
Connected next stepOpen the most relevant production tool and verify the decision with a working output.
Review the headings, sources, implementation artifact, and update record for this guide as structured JSON.
Download guide evidence ↓- Guide
- Favicons in Firefox: Tabs, Bookmarks, SVG, and Cache Testing
- Coverage
- Client behavior can change by browser, operating system, platform version, cache state and deployment configuration. Unperformed manual observations are not claimed.
Questions, answered
Does Firefox support SVG favicons?+
Firefox participates in the standards-based rel=icon candidate model. Keep SVG self-contained and offer raster and ICO fallbacks for the wider ecosystem.
Why does a fresh profile show the new icon?+
That result strongly points to cached site data in the older profile rather than a missing production file; verify the network response before clearing data.