How to Change or Reset Firefox Default Browser Agent

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A user agent is a line of code that tells websites what type of browser and operating system you are using.

Changing the User Agent string can be useful in some cases when a website’s functionality is locked for the specific platform and you need to bypass the restriction. Needless to say, changing the User Agent string can be useful for web developers. Below you will learn how to change the user agent string in Mozilla Firefox. This can be done either with an extension or natively.

Traditionally, the user agent string is used by web developers to optimize their web applications for different devices. This allows developers to differentiate between different categories of devices such as tablets, phones, desktops and laptops and many others. The user-agent chain can provide Web servers with certain information about the user’s operating system and browser version.

Resetting Firefox’s Default User Agent

How to reset your Firefox User Agent:

  1. Type about:config in the address bar and press Return.
  2. A warning page may be displayed. Click Accept Risk and go to the about:config page.
  3. Search for the User Agent by entering it in the Search Preference Name field.
  4. For each of these settings, click the “Reset Fx71aboutconfig-ResetButton” or “Delete Fx71aboutconfig-DeleteButton” button, if they exist:

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  • general.useragent.extra.firefox
  • general.useragent.extra.productName – where productName can be the name of some third party software (e.g. microsoftdotnet).
  • general.useragent.locale
  • general.useragent.override

How to Change the User Agent of your Firefox Browser

This option is buried on the about:config page of Firefox.

  • To access the about:config page, type about:config in the Firefox address bar and press Enter. You will see a warning – be careful, if you change any settings here, you may damage the Firefox settings.
  • Type useragent in the filter field. We are looking for the reference general.useragent.override, but it probably doesn’t exist on your system.
  • To create the preference, right-click on the about:config page, point to New and select String.
  • Name the preference general.useragent.override .
  • Enter the desired user agent as the preference value. You must search the web for the desired user agent and enter it accurately. For example, the following user agent is used by Googlebot, Google’s indexing robot:
    • Mozilla/5.0 (compatible; Googlebot/2.1; +
  • This setting applies to every tab you open and remains in effect until you change it, even if you close and reopen Firefox.
  • To reset Firefox to the default user agent, right-click the general.useragent.override setting and select Reset.


Note that changing the user agent does not change the way the web browser displays the pages itself, unless user agent-specific content is provided.

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