How to reset the default user agent on Firefox

No one has helped translate this article yet. If you already know how localizing for SUMO works, start translating now. If you want to learn how to translate articles for SUMO, please start here.

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.

You can change Firefox's user agent to trick outdated websites into thinking that you're using a different version of the browser. Web developers might do this to see how their websites will appear on different versions of a browser. Sometimes, add-ons and other installations can change your user agent without your knowledge. In any case, it's important to switch it back to the default user agent to display most websites correctly.

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 68 on Windows 7 (64-bit) would appear as:
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0

Note: If your user agent shows a previous Windows version, such as NT 6.0 (Windows Vista) instead of NT 6.1 (Windows 7), 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 all items are deselected in the "Compatibility" tab of the Properties window.

To reset your user agent:

  1. In the address bar, type about:config and press EnterReturn.

    • The about:config "This might void your warranty!" warning page may appear. Click I accept the risk! 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.
  • 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


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

  1. Click the Library button 57 library icon , click History and select Clear Recent History….
  2. In the Time Range to clear: drop-down, select Everything.
  3. Click the arrow next to Details to display the list of items that can be cleared.
  4. Select both Cookies and Cache.
  5. Click Clear Now.
  1. Click the Library button 57 library icon , 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.
  4. Click Clear Now.

// These fine people helped write this article:AliceWyman, TyDraniu, Swarnava Sengupta, user669794, Joni. You can help too - find out how.

இந்த கட்டுரை பயனுள்ளதாக இருந்ததா? தயவு செய்து காத்திருக்கவும்...

Volunteer for Mozilla Support