User-Agent Spoofer by ThatPrivacyFreak
Spoof the HTTP and JavaScript User-Agent.
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About this extension
User-Agent Spoofer can spoof your HTTP User-Agent and the normal JavaScript
Some websites deliberately create a sandboxed iframe and read its separate
This is a limitation of Firefox's separate browsing-context behavior rather than a failure of the normal User-Agent spoofing.
Please be aware of this limitation before installing. User-Agent Spoofer does not promise that every browser fingerprinting or anti-spoofing test can be defeated.
There’s an Easter egg hidden inside… can you find it?
navigator User-Agent, but Firefox has one known limitation.Some websites deliberately create a sandboxed iframe and read its separate
navigator object. Firefox can expose the underlying User-Agent from this isolated context even when the normal page's User-Agent has been spoofed.- ✅ HTTP
User-Agentrequest header - ✅ Normal page
navigator.userAgent - ✅ Normal page
navigator.appVersion - ✅ Other supported
navigatorproperties - ✅ Custom User-Agent profiles
- ⚠ Highly isolated/sandboxed iframe User-Agent detection may still reveal the real browser User-Agent.
This is a limitation of Firefox's separate browsing-context behavior rather than a failure of the normal User-Agent spoofing.
Please be aware of this limitation before installing. User-Agent Spoofer does not promise that every browser fingerprinting or anti-spoofing test can be defeated.
There’s an Easter egg hidden inside… can you find it?
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Permissions and data
Required permissions:
- Access your data for all websites
Data collection:
- The developer says this extension doesn't require data collection.
More information
- Add-on Links
- Version
- 1.0.0
- Size
- 521.27 KB
- Last updated
- 6 days ago (Sep 16, 2026)
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