There are several aspects to browser performance. At the simplest level, there's the question of how quickly a browser can render a page. Here, the "Gecko" rendering engine used by Firefox is well known to be faster than the IE8 internal engine Microsoft admits as much on its own "browser comparison" page.
However, the company also makes the valid point that, on a modern PC, both can lay out complex HTML and CSS pages in the blink of an eye; the limiting factor is more likely to be the speed of your internet connection. The company argues that, in terms of performance, the two browsers are therefore tied.
Yet rendering speed isn't the only factor to consider. RAM usage is important too, especially if you're looking for a browser to run on a low-power netbook. To see which browser is more memory efficient, we carried out a simple test, opening a list of tabs and closing them again. When first loaded, IE8 consumed just 13MB of system memory, but once we'd opened all our sites including a Google search and a YouTube video this had gone up to 116MB. Firefox required a higher 28MB to load up, but then consumed only 91MB with all tabs open. On a modern system, 25MB here or there is insignificant, so for simple surfing the two browsers are indeed more or less tied.
A final consideration is JavaScript performance. Many modern websites use JavaScript to deliver "web applications" that run in your browser, and the more rapidly your browser can execute JavaScript code, the more smoothly these applications will run.
To measure JavaScript performance we used the independent SunSpider benchmark, which executes and times a series of common JavaScript operations. Here the gap was definitely significant: IE8 took an average of 3.9 seconds to complete the benchmark on our test system, while Firefox whizzed through it on the same PC in just 0.9 seconds.
The SunSpider benchmark exposes IE8's relatively poor JavaScript performance.
