How do I tell if I have the 32-bit or 64-bit Firefox?

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This article only applies to Firefox on Windows.

Note: This article applies to Firefox on 64-bit operating systems with Windows 7 or above. See Microsoft's instructions here and here to find operating system information for your version of Windows.

In addition to the 32-bit version of Firefox, a 64-bit version of Firefox is available for 64-bit operating systems, on Windows 7 or above. See this blog post for details. This article explains how to determine whether you are using the 32-bit or 64-bit version of Firefox.

User agent

The user agent identifies your browser to websites and contains information about your operating system and browser version. This can be an easy way to identify which version of Firefox is running.

To find your user agent, click the Firefox menu button New Fx Menu, click help Help-29 and select Troubleshooting Information. This will open the Troubleshooting Information page.

User Agent Fx42.0

In the Application Basics section of this page, find the User Agent entry and look at the information enclosed within the parentheses. If your user agent contains WOW64, you are running the 32-bit version of Firefox. If your user agent contains Win64; x64, you are running the 64-bit version of Firefox.

Windows program listing

You can also check the installed version of Firefox from the Windows list of installed programs. Open the Windows Control Panel, click on Programs, then Programs and Features.Open the Windows Settings, click on System, then Apps & features. This will load a list of software that is currently installed on your computer.

To determine whether you have the 32-bit or 64-bit version of Firefox installed, locate Mozilla Firefox in the list of programs. The program name will include the Firefox version and, in parentheses, the bit version and language. If the program name contains x86, the 32-bit version of Firefox is installed. If the program name contains x64, the 64-bit version of Firefox is installed.
Note: It's possible to have both 32-bit and 64-bit versions of Firefox installed.