The stock Firefox browser, with that I mean the releases that are available for download on the Mozilla website directly, can be run on 32-bit and 64-bit Windows operating systems. While that is the case, Mozilla did offer a 32-bit version for Windows until 2016. Find out how to download and install 64-bit Firefox here.
64-bit versions of Firefox were available prior to 2016 but they were made available by Mozilla for Linux distributions and Mac OS X only officially.
The 64-bit version of Windows was not offered by Mozilla on the main download site and you could not really find it advertised anywhere on the site; this did not mean that the version did not exist as it was build automatically and pushed to the FTP server.
Before we look at download options, it is necessary to find out about the differences between 32-bit and 64-bit versions of Firefox, or applications in general.
Note: You may find the guides How to upgrade Firefox 32-bit to 64-bit, and Time to make the switch to 64-bit Firefox on Windows useful as they highlight upgrade options and reveal how you can find out which version of Firefox you run.
First, it needs to be mentioned that most 32-bit applications run fine on 64-bit operating systems, but that no 64-bit application will run on a 32-bit system.
One of the advantages of 64-bit software is that it may have more memory at its disposal, provided that that enough is installed on the 64-bit operating system. The physical memory limit of 32-bit versions of Windows is 4 Gigabyte, while 64-bit versions of Windows support more than that. How much more depends on the version you are using. Windows 8 Professional 64-bit supports 512 Gigabyte for example, while Windows 7 Professional 64-bit 192 Gigabyte.
Technically, the 4 Gigabyte limit refers to the addressable memory space which the installed RAM, video cards, PCI memory range and other factors attribute to. That's the reason why you won't see 4 Gigabytes of available RAM on 32-bit versions of Windows even though you have installed that much, as part of it is used by other components. (see this for a detailed explanation)
If you are running Firefox on a 32-bit Windows operating system, it can use 3 Gigabytes of memory at the most. If you run it on a 64-bit Windows system, it can use up to 4 Gigabytes of RAM.
While it is unlikely that most users will run into the limits, new technologies such as web gaming and other real-time activities may increase the RAM needs of the browser, and may push browsers towards 64-bit eventually.
A 64-bit version of Firefox that runs on a 64-bit Windows has much larger limits, from about 8 Terabytes to up to 128 Terabytes. (see this page for more information)
It may take some time until we get there in regards to consumer PCs, but it is not that unlikely anymore that PCs have more than 4 Gigabyte of RAM installed.
Conclusion: if Firefox uses a lot of RAM on your system, you may want to consider using a 64-bit version of the browser to avoid the memory limit.
There may be other benefits: 64-bit applications can perform 64-bit register operations, which is faster than performing the same operation on a 32-bit system. There may also be security benefits to running 64-bit programs as opposed to running 32-bit programs.
If you compared 32-bit versions of Firefox to their 64-bit builds on Windows in the past, you would have found out that they would differ in several aspects:
If you look at the situation right now, you will notice that a lot of things have changed.
Firefox 64-bit for Windows is offered as the primary version by Mozilla now. It is available for the release channel and supported by Mozilla. Plugins are no longer an issue as Mozilla dropped support for them (except Flash) recently.
You can download the 64-bit version of Firefox from Mozilla's official download site. This was not possible in the past but the installer that the organization provides on its main site will install the 64-bit version of Firefox if the system supports it.
If you run the browser on a system with Firefox installed, you will notice that it will share the profile with that version automatically. You cannot run both versions side by side at the same time, unless you run one of the two versions with the -no-remote -p test command (test is the name of the second Firefox profile that you want to load).
Third-party forks of Firefox exist that provide access to a 64-bit version. You can download the 64-bit version of Pale Moon for example. The browser is compatible with all 64-bit operating systems from Windows Vista on and supports all the things that Firefox supports as well.
This may also be an option for Firefox users who do not like the new Australis interface that will be enabled in Firefox 29, as Pale Moon won't switch to that.
Mozilla moved from supporting 32-bit versions of Firefox for Windows exclusively to prioritizing 64-bit of Firefox for Windows in recent years. While it is still possible to download a 32-bit copy of Firefox, it is the 64-bit version that is offered by default now.Advertisement
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