Although Mozilla has long had 64-bit versions for OS X and Linux, the developer shelved work on one for Windows in November 2012, only to recant and restart the project a month later. Its path to a 64-bit Firefox for Windows has been contorted. Mozilla Firefox (bit) has had 9 updates within the past 6 months. Mozilla was the last holdout among the top five browser builders.

Opera Software, the Norwegian browser maker known for its same-named desktop flagship, also offers a 64-bit edition on Windows.

Google, for example, shipped a Windows 64-bit Chrome in August 2014 and one for OS X in November of that year, while Apple's Safari and Microsoft's Internet Explorer (IE) have had 64-bit editions on OS X and Windows since 20, respectively. The appearance today of the Firefox 43 ends Mozilla's climb to catch up with rivals, who had offered 64-bit browsers long before, in some instances years. The biggest advantage of a 64-bit browser on a 64-bit operating system - like Windows and Apple's OS X - is that it can address more than the 4GB of memory available to a 32-bit application, letting users keep open hundreds of tabs, and run larger, more sophisticated Web apps, notably games.

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