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A user agent 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. If websites tell you that your browser is outdated or incompatible even though Firefox is up to date, an incorrect user agent may be the cause. This article explains how to fix problems with your Firefox user agent so that websites work properly.
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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 
, click and select . This will open a page with the address about:support. The Application Basics section will show your current Firefox version and will include a User Agent entry. For example, the default user agent entry for Firefox 83 on Windows 10 (64-bit) would appear as:
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:83.0) Gecko/20100101 Firefox/83.0
Sites such as What is my user agent? (WhatIsMyBrowser.com) and What's my user agent? (whatsmyua.info) can also show you the user agent detected by websites.
Add-on issues
Add-ons such as the User-Agent Switcher extension can change the user agent that websites detect. See if you can restore the default user agent in your extension settings. You can also temporarily restart Firefox with all add-ons disabled (see Diagnose Firefox issues using Troubleshoot Mode for details) and, if the problem goes away, disable or remove any add-on you think may be the cause. If you can't resolve the problem this way, follow the steps below to reset the default user agent.
Reset the default Firefox user agent
You can reset your user agent as follows:
Only proceed if you are comfortable with advanced settings and understand the potential impacts.
- Type about:config in the address bar and press EnterReturn.
A warning page may appear. Click to go to the about:config page. - Search for useragent by typing it into the Search preference name field.
- Click the Reset or Delete 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
See Configuration Editor for Firefox for more information about using the about:config page to reset or delete preferences.
After resetting your user agent, you may need to restart Firefox and clear your cookies and cache:
- Click the menu button to open the menu panel.
- Click and select
- In the Time range to clear: drop-down, select Everything.
- Below the drop-down menu, select both Cookies and Cache. Make sure other items you want to keep are not selected.
- Click .
- Click the menu button to open the menu panel.
- Click and select
- In the When: drop-down, select Everything.
- Below the drop-down menu, select both Cookies and site data and Temporary cached files and pages. Make sure other items you want to keep are not selected.
- Click .
