In terms of speed alone, Apple is taking some steps to position its Safari browser to pass Google’s Chrome. But Mozilla’s Firefox has been running a different race.

Apple has been upgrading its WebKit open source browser engine to speed up Safari’s JavaScript processing in the OS X versions.

JavaScript is key to interactivity on Web pages, and a browser’s speed in handling JavaScript directly impacts how fast users feel a website is running.

WebKit, an open source browser engine for rendering web pages, is used in Safari. It had been used in Chrome, but now Google uses an WebKit offshoot called Blink.

The upgrades, called FTLJIT, are being made to the Nitro JavaScript engine in Apple’s WebKit.

But InfoWorld points out a pertinent fact: FTLJIT is still fairly “experimental,” and, although available in Safari’s WebKit, “it’s not actually turned on yet.”

According to tests done by the Mozilla team, Safari with FTLJIT enabled passes Chrome in running JavaScript for some benchmarks. Still, Mozilla’s Firefox takes the cake when running JavaScript that has been optimized with asm.js.

Mozilla’s asm.js project has developed a version of JavaScript to dramatically improve performance. It is intended, for instance, to allow high performance games to be run from the Web without plugins.

“Only Mozilla’s SpiderMonkey [JavaScript engine] honors asm.js-specific optimizations,” InfoWorld points out, “and right now no other browser maker has elected to follow Mozilla’s lead.”