How to switch to a 64-bit Firefox on Windows

I recently wrote about 64-bit Firefox builds on Windows, explaining why you might want to switch — it can reduce the likelihood of out-of-memory crashes — and also some caveats.

However, I didn’t explain how to switch, so I will do that now.

First, if you want to make sure that you aren’t already running a 64-bit Firefox, type “about:support” in the address bar and then look at the User Agent field in the Application Basics table near the top of the page.

• If it contains the string “Win64”, you are already running a 64-bit Firefox.
• If it contains the string “WOW64“, you are running a 32-bit Firefox on a 64-bit Windows installation, which means you can switch to a 64-bit build.
• Otherwise, you are running a 32-bit Firefox on a 32-bit Windows installation, and cannot switch to a 64-bit Firefox.

Here are links to pages contain 64-bit builds for all the different release channels.

• Release
• Beta
• Developer Edition
• Nightly:  This is a user-friendly page, but it only has the en-US locale.
• Nightly: This is a more intimidating page, but it has all locales. Look for a file with a name of the form firefox-<VERSION>.<LOCALE>.win64.installer.exe, e.g. firefox-50.0a1.de.win64.installer.exe for Nightly 50 in German.

By default, 32-bit Firefox and 64-bit Firefox are installed to different locations:

• C:\Program Files (x86)\Mozilla Firefox\
• C:\Program Files\Mozilla Firefox\

If you are using a 32-bit Firefox and then you download and install a 64-bit Firefox, by default you will end up with two versions of  Firefox installed. (But note that if you let the 64-bit Firefox installer add shortcuts to the desktop and/or taskbar, these shortcuts will replace any existing shortcuts to 32-bit Firefox.)

Both the 32-bit Firefox and the 64-bit Firefox will use the same profile, which means all your history, bookmarks, extensions, etc., will be available in either version. You’ll be able to run both versions, though not at the same time with the same profile. If you decide you don’t need both versions you can simply remove the unneeded version through the Windows system settings, as normal; your profile will not be touched when you do this.

Finally, there is a plan to gradually roll out 64-bit Firefox to Windows users in increasing numbers.