3 Ways to Fix the ReferenceError: Browser is not Defined

Quickly solve the browser not defined console error

by Megan Moore
Megan Moore
Megan Moore
Megan is a Windows enthusiast and an avid writer. With an interest and fascination in all things tech, she enjoys staying up to date on exciting new developments... read more
Fact checked by Alex Serban
Alex Serban
Alex Serban
Windows Server & Networking Expert
After moving away from the corporate work-style, Alex has found rewards in a lifestyle of constant analysis, team coordination and pestering his colleagues. Holding an MCSA Windows Server... read more
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  • Users report getting the ReferenceError: browser not defined when trying to create extensions for Chrome and Firefox.
  • This error usually occurs when there is a browser referenced that is not accessible in the script.
  • Making sure your browser is updated and disabling any addons can help solve the error.
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Most popular browsers offer access to the console so developers and programmers can access the code for web design and testing. However, users have reported receiving the ReferenceError: browser not defined. Try our solutions below to fix the issue.

Why am I getting the browser not defined error?

The ReferenceError: browser not defined occurs when there is a reference to a non-existent browser somewhere in the code when trying to create an extension. Declare the browser in reference or make sure it’s accessible in the script.

Browser not defined.

The browser variable declared within a function is not available outside of that function which could lead to the error. Defining the browser outside of the scope of function will make it accessible. Another possible cause could be a misspelling of the browser global variable.

Here are some variations of the error for browsers:

  • browser is not defined in Firefox
  • referenceerror: browser is not defined in Chrome

For other platforms:

  • browser not defined in JavaScript
  • browser not defined reactjs
  • referenceerror: browser is not defined webdriverio
  • browser is not defined adblock
  • browser is not defined puppeteer
  • referenceerror: browser is not defined mocha

Quick Tip:

There are several causes of browser errors, but we noticed minimized issues in the Opera browser. Switch to Opera with all of your saved data from your existing browser and test the connection.

A browser’s undefined failure might be caused by an outdated version of the browser, but not in Opera. Since it’s also with a built-in VPN, you may switch servers for a more stable connection.


Automatic updates, stable and wide connections through the proxy VPN servers.

How can I fix the browser not defined error?

1. Update your browser

  1. Click on the browser menu located in either the top left or right corner and select Help. Open the menu and select Help.
  2. Click About. Click on About.
  3. Here your browser will automatically check for any updates. If there is an update, click Update. Update your browser to fix the browser not defined error.

If your browser is out of date, then issues may arise in the console. Regularly check for updates in your browser to avoid any future issues.

2. Disable add-ons

  1. Click on the browser menu located in either the top left or right corner and select Settings. Open browser settings to fix browser not defined error.
  2. Select Extensions or Addons. Open extensions.
  3. Go through and toggle each extension off. Disable extensions to fix browser not defined error.

Users report that disabling add-ons like Ad-block has solved the problem. Disabling all of your extensions may fix the issue

3. Change the namespace

If you’re running into the ReferenceError: browser is not defined in Google Chrome, then you will need to change the namespace with callbacks from browser.* to chrome.* for cross-compatibility. You can do this by manually changing the namespace and callbacks to chrome.* which will work in both Chrome and Firefox.

Use the WebExtension polyfill to fix browser not defined error.

Users can also use a shim or polyfill to convert the browser.* namespace to chrome.* with callbacks for Chrome. One shim to use is WebExtension which offers a lightweight polyfill library WebExtension APIs in Chrome.

We hope one of the above solutions helped you fix the browser is not defined. error. If you’re looking for recommendations for the best browsers for developers, we have a guide for that. Let us know in the comments which solution worked for you or if you have a suggestion for a different solution.

Still having issues? Fix them with this tool:


If the advices above haven't solved your issue, your PC may experience deeper Windows problems. We recommend downloading this PC Repair tool (rated Great on TrustPilot.com) to easily address them. After installation, simply click the Start Scan button and then press on Repair All.

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