How to reset the default user agent on Firefox

A user agent is a line of code that tells websites what type of browser and operating system you're using. This information helps the web server deliver content that's compatible with your browser.

User agent issues

You can change Firefox's user agent to trick websites into thinking that you're using a different browser or operating system. Web developers might do this to see how their websites will appear on different systems and browsers. Sometimes, add-ons and other installations can change your user agent without your knowledge.

Websites may not display correctly or may show a message that your browser is outdated or incompatible, based on the detected user agent. It's important to switch Firefox back to the default user agent so that websites work properly.

View your user agent

To view your user agent, click the Firefox menu button Fx57Menu , click Help Fx57Help and select Troubleshooting Information. This will open a page with the address about:support. The Application Basics section will include a User Agent entry. For example, the default user agent entry for Firefox 72 on Windows 10 (64-bit) would appear as:
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:72.0) Gecko/20100101 Firefox/72.0

Note: If your user agent shows a previous Windows version, such as Windows NT 6.1 (Windows 7) instead of Windows NT 10.0 (Windows 10), make sure you are not running Firefox in Compatibility mode. You can open the Properties of the Firefox desktop shortcut from the right-click context menu. Check the "Compatibility" tab and make sure that the compatibility mode option is not selected.

Reset the default Firefox user agent

To reset your user agent:

  1. Type about:config in the address bar and press EnterReturn.
    A warning page may appear. Click I accept the risk!Accept the Risk and Continue to continue to the about:config page.
  2. Search for useragent by typing it into the Search field.
  3. Right-clickHold down the control key while you click on each of these preferences, if they exist, and select Reset from the context menu.
  1. Type about:config in the address bar and press EnterReturn.
    A warning page may appear. Click I accept the risk!Accept the Risk and Continue to continue to the about:config page.
  2. Search for useragent by typing it into the Search preference name field.
  3. Click the Reset Fx71aboutconfig-ResetButton or Delete Fx71aboutconfig-DeleteButton button on each of these preferences, if they exist:
  • 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
  • general.useragent.security

reset_ua1.png See Configuration Editor for Firefox for more information about using the about:config page to reset or delete preferences.

Note: If the above solution doesn't resolve the problem, check whether you have the privacy.resistFingerprinting preference set to true and, if so, double-click on the preference to reset it to false. This setting can change the user agent and cause this type of issue. For more information, see Firefox's protection against fingerprinting.

After resetting your user agent, you may need restart Firefox and clear your cookies and cache:

  1. Click the Library button 57 library icon on your toolbar. (If you don't see it there, click the menu button fx57menu then click Library.) Click History and select Clear Recent History….
  2. In the Time Range to clear: drop-down, select Everything.
  3. Below the drop-down menu, select both Cookies and Cache. Make sure other items you want to keep are not selected.
  4. Click Clear Now.

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