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I read about EFF's Panopticlick project to see how unique your webbrowser's headers are. I would like to anonymize that a bit.

My current User Agent is

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.7) Gecko/20100106 Ubuntu/9.10 (karmic) Firefox/3.5.7

I would like to make that more anonymous, however I still wanted to be counted as a Firefox and Ubuntu user.

  • How can I change my User Agent in Firefox?
  • What should I change it to so that it's less unique, but will be counted as a Firefox user and a Ubuntu user on web analytics software?

I know that there is no guarantee that I will be counted a Firefox/Ubuntu user, just something that 'works most of the time' would be sufficent.

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9 Answers 9

You can use this addon to change/create custom User Agent's.

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Also the general.useragent.override setting in about:config will do the same. –  whitequark Feb 2 '10 at 13:55

First, why would you want this? Nobody can tell who you are from your User-Agent, your IP address is far more interesting.

You could change your version numbers, but that won't achieve much.

To get to general.useragent.override, you type about:config in your address bar, give your consent, and then search for it, right click and edit.

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3  
Because as paranoid as it sounds there was a news article a little while back that pointed to a study that showed they could identify people with UserAgent strings + some other info from the browser without looking at the IP. –  MrStatic Feb 2 '10 at 14:45
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Also you gotta love someone who takes someone elses comment and posts it as an answer. –  MrStatic Feb 2 '10 at 15:17
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Did you take a look at your browser's uniqueness at panopticlick.eff.org? Mine: Your browser fingerprint appears to be unique among the 514,535 tested so far. (Of course, it's not just the User Agent that makes up that figure.) –  Arjan Feb 2 '10 at 15:28
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@Arjan van Bentem. The User-Agent string submitted by my browser is not the most unique thing in the world, my System-fonts list is far more unique (a factor of 10!). If is mostly the combination of stuff that makes it unique. An anonymizing proxy is still the best solution IMHO –  Thom Wiggers Feb 2 '10 at 18:06
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I think you're missing the point. A proxy does not change the things a browser emits. –  Arjan Feb 2 '10 at 18:24

Since it's Ubuntu, I would imagine there are many people with the same Firefox version. So your original is actually better than, for example, Mozilla/5.0 (Linux) Gecko Ubuntu Firefox, because the original is a lot more common.

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Partially anonymizing your user agent actually makes your header more unique, not less. (Think of a stripe-less zebra in a herd.)

However, if you insist I would start by removing all specific minor version numbers as they can be used to target known vulnerabilities. I would leave alone the strings likely used by applications to determine browser compatibility.

So

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.7) Gecko/20100106 Ubuntu/9.10 (karmic) Firefox/3.5.7

becomes something like this:

Mozilla/5 (X11; U; Linux i686; en-US) Gecko/2010 Ubuntu/9.10 (karmic) Firefox/3.5
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1  
Major +1 for changing the user agent making you more noticeable. –  ceejayoz Feb 2 '10 at 17:23
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...unless one changes it into something more common. That's what the question is about: can it be made more common, without hiding one is using Firefox on Ubuntu. –  Arjan Feb 2 '10 at 19:02
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Having missing data in the user agent string is LESS common then using a default string. If you don't want to give away version numbers for fear of attracting hacks then messing with your user agent could possibly help. However, changing it to a string that almost no browsers actually use by default makes it MORE unique and therefor easier to pick out of the crowd. In this case I would use the default string for a fresh install of the OS in question. It doesn't give away your current version numbers and is likely to be in use by LOTS of browsers. –  Chris Nava Aug 24 '11 at 6:11

Answer to the first question:

Set the user agent in Firefox by changing setting general.useragent.override (general.useragent.extra.firefox will not work in this case as it only adds to the current user agent string):

  1. Type about:config in the address bar and press Enter
  2. Click the accept button on the warning page.
  3. Type useragent in the filter to see if general.useragent.override is defined (it is not by default)
  4. Create general.useragent.override if it does not exist. Right click or Shift + F10 in the lower part of the panel, select New and String and type "general.useragent.override" (see first screenshot below)
  5. Change the value to something like googleinstantisreallyirritating or www.google.com (by double clicking or pressing Enter when the setting is selected). The original setting is something like Firefox/3.6.

This was tested on Firefox 11 (but the screenshots are from Firefox 3.6).

enter image description here

The result is something like:

enter image description here

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What you are looking for is not really to change the user-agent, but to "scrub" your outgoing traffic of any HTTP headers that could potentially identify you. You want an anonymizing proxy server.

I've used an old program which I doubt is being updated any longer called Proxomitron on Windows systems in the past (around 2001, 2002). Privoxy (often used in combination with Tor) is useful for this purpose, currently updated, and also blocks a couple of ads as well.

Note that details of your system can leak through JavaScript and browser extensions. For the most anonymous browsing you want to disable JavaScript, not use Flash (or at least selectively enable them for trusted sites using NoScript), and whitelist cookies on a site-by-site basis.

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This can be solved if you redefine how you want to be anonymized. You're already anonymous in the sense that your user agent string won't identify you by your human name. If you mean you do not want to be recognized as a previous visitor to a website, one option would be to change your browser's user agent string between requests. Sure, you would still be identified as being unique, but not identifiable with regards to a previous visitor. I'm not sure if there are Firefox add-ons that do this, it's just an idea, but it could be done. The version numbers could be randomized, or simply incremented. The other suggestions are probably more wise, but perhaps this idea will be useful somehow.

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The most anonymous way would probably be to go for a very common User Agent string.

IMHO being less recognizable and having Linux as user agent is a bit of a contradiction, unless in your cluster a lot of people use Linux.

that being said, I dont know how but I would try to go for a very common user agent, maybe what TOR is using, and use that.

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Very simple, either go to your firefox profile folder and create a file called user.js and place the following code in your user.js file.

user_pref("general.appversion.override", "5.0 (X11)");
user_pref("general.buildID.override", "20140421162246");
user_pref("general.oscpu.override", "Linux i686");
user_pref("general.platform.override", "Linux i686");
user_pref("general.useragent.override", "Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Firefox/24.0");

Upon first boot up, the above settings will be replaced with your custom settings, obviously change them to suit your needs, if they are ever inadvertently modified as long as the user.js is still in your Firefox profile, they will be replaced upon next boot up. Another option is to load up about:config in the Firefox browser and manually alter those settings. you can't just modify one, you have to modify all of them, modifying the user agent to say Linux but not modifying oscpu so it still says Windows would not further anonymity you but but make it way easier to fingerprint and identify you.

Any website which uses browser fingerprinting can still identify your browser and operating system correctly, all browsers and operating systems send data in a certain manner, regardless of your http headers sent, analyzing this data can still correctly identify this information.

Bottom Line: Modifying HTTP headers may protect you in 5 or 10% of hacking attempts by websites run by amateurs by confusing them which vulnerabilities to check for, but any website designer with a half decent knowledge of website design and programming will still be able to correctly identify your OS and browser and you will actually be increasing your uniqueness by trying to fool them not decreasing it.

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