Masking Agent is a Firefox add-on that hides your platform detais.
*** Discontinuation ***

*** I will discontinue support for this add-on, August 1, 2015. ***
*** If you want to take over support and/or further development, please contact me here ***


Your web browser reveals more information than you think. Notably, with each web access the browser reveals the Operating System (e.g. Windows 8.1, Mac OS X 10.9, or Ubuntu 14.04) and the CPU. Check the Masking Agent demo for your current configuration. Mostly, the information about your platform is not needed to browse the web, at all. If you're using an older, more vulnerable computer, you may not want to be so generous with this information. In general, it's a good idea to control the information that you transmit.

There are several Firefox add-ons available that let you mimic a completely different browser, i.e. browser application and platform. But none of them meet my requirements:

So, I made Masking Agent.


The information shown below is available to every web site you visit. If you don't have Masking Agent installed and enabled, your platform details are plainly visible. Revisit this page with Masking Agent installed to see the differences.

JavaScript navigator.appVersion
(Browser compatibility)
(requires JavaScript)
JavaScript navigator.oscpu
(OS/CPU platform details)
(requires JavaScript)
JavaScript navigator.platform
(Platform summary)
(requires JavaScript)
JavaScript navigator.userAgent
(User-Agent browser signature)
(requires JavaScript)
HTTP User-Agent
(User-Agent browser signature)
CCBot/2.0 (


Masking Agent is hosted at a Mozilla add-on page:

You can download it directly:

Frequently Asked Questions
Known Issues
Resetting Masking Agent

When the add-on is not working as described:

  1. In Firefox, go to your installed add-ons in the Add-ons Manager and find Masking Agent.
  2. Click the "Disable" button of this add-on.
  3. Open a new tab or window, and navigate to address about:config?filter=general.*.override
  4. From the displayed list of preferences, reset the following preferences, i.e. right-click each preference separately, and select "Reset" from the context menu:
    • general.appversion.override
    • general.oscpu.override
    • general.platform.override
    • general.useragent.override
  5. Return to your installed add-ons and re-enable Masking Agent.

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