Here is the full changelog for Firefox Developer Edition 38:

The end result means it is harder for malicious web content to exploit the browser. The increased address space also lets Firefox use hardware memory protection and improves the effectiveness of ASLR (address space layout randomization). This significantly speeds up how quickly JavaScript code can run. 4GB isn’t the only limit worth remembering: Heap sizes, for example, are recommended to be 512MB in a 32-bit browser, while they can go up to 2GB in a 64-bit version of Firefox.Īs for execution time, Mozilla says 64-bit Firefox is faster because it can access new hardware registers and instructions. “For some of the largest of these apps, a 64-bit browser means the difference between whether or not a game will run,” Mozilla says. Here’s a game built with Epic Games’ Unreal Engine running on the Firefox Developer Edition: Browser-based games, for example, especially those with native-like gameplay, are often much larger than typical online apps mainly because they have high-quality assets that must be stored in memory for synchronous loading.

A 32-bit browser is limited to 4GB of address space, and while this may be surprising to some, web applications are getting bigger and bigger to the point where this can actually be an obstacle.