Mozilla rolls out dev-only 64-bit Firefox for Windows

Mozilla has revved its Developer Edition version of the Firefox to 38 and for the first time introduced a full 64-bit build of the browser for Windows.

Aside from matching Google, which has offered a 64-bit version of Chrome since last August, Mozilla’s native 64-bit build of Firefox boasts three key features: faster execution speed, better security, and the ability to run larger programs.

An advantage of using 64-bit applications is their use of a larger address space on a server or desktop. For a browser like Firefox, this translates into having more tabs open at once and running more ambitious in-browser applications. But other advantages of 64-bit apps include better leveraging of address space layout randomization (ASLR), a common technique for protecting against software exploits. Mozilla touts this as a boon for 64-bit Firefox, and Chrome’s 64-bit edition has similar functionality.

The third big boon for a 64-bit Firefox is increased execution speed for JavaScript — specifically, JavaScript written using Mozilla’s asm.js extensions, which allow highly optimized JavaScript to compile to code that runs close to the speed of native C. Mozilla has touted asm.js for porting C/C++ code to the Web, and Microsoft has elected to include extensions for asm.js in its Chakra JavaScript engine. (Chrome may be following suit as well.)

Mozilla provided a big example for 64-bit asm.js: “browser-based games that deliver performant, native-like gameplay, such as those built with Epic Games’ Unreal Engine,” featuring assets that are “often much larger than we expect from traditional Web applications.” With 64-bit address space at one’s disposal, it’s easier to load and process those assets, but there are ostensibly other applications for a larger address space beyond gaming.

Firefox was previously available in 64-bit editions for Mac OS X and Linux, but Windows still accounts for the majority of Firefox’s market share. An earlier effort to put a 64-bit edition of Firefox into the hands of Windows users stalled in 2012, with the lack of 64-bit plug-ins for Firefox cited as a big reason.

But strong backlash from users prompted Mozilla to reconsider, although it has made no promises as to when a 64-bit version will be released to the general public. Native HTML5 functionality has eclipsed traditional plug-ins — from replacing Flash to playing back encrypted video content — so it’s easier to deliver a native 64-bit browser.

Mozilla is holding off on delivering a 64-bit browser for users to focus on higher-priority projects — for example, Firefox OS, set to debut next year on phones in major markets.