Mozilla: Internet Explorer 7 more memory-intensive than Firefox 3

Graphical analysis of a comparison between IE and two versions of Firefox [source: Pavlov.net]

The developers at Mozilla have put a lot of effort into tackling the memory requirement problem when developing the third version of their Firefox web browser. On the appearance of the fourth beta version of Firefox 3, they have proudly announced a "substantial improvement in the use of memory". Stuart Parmenter, a Firefox developer also known as Pavlov, describes how it was done in his weblog. On top of that, he writes, a test showed that after Internet Explorer 7 closes it releases no memory, while the beta 4 of Firefox version 3.0, shows a substantial improvement in memory handling, compared with the current Version 2.0.0.12.

For the purpose of the test, 29 different web sites were loaded in their own windows using the three web browsers, running under Windows Vista, over eleven cycles. After all windows but one had been closed again and a few minutes had elapsed, the developers checked whether the browsers were still occupying memory, and how much they had released. A proxy server was used in the tests in order to ensure that the identical content was loaded.

Going by what "Pavlov" writes, it looks as though the Mozilla developers have at least got a partial grip of the problem of memory fragmentation, a problem that arises especially with programs that run for a long time. In order to achieve this, the number of different memory areas occupied by Firefox when it starts up has been reduced. Part of the effort was a revision of the "Jemalloc" technology developed by Jason Evans, which is being used in the beta 4 for Windows and Linux. Under Windows Vista, it is claimed to reduce memory requirement by 22 per cent.

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The Firefox cache technology was also revised: this ensures, for example, that the content of a previously visited page is quickly redisplayed. The cache for rapid back/forward navigation deletes the web-site content it holds 30 minutes after the last call. There are similar time limits at other points, too. The data of decompressed images that have been held for some time in the background behind a tab are cleared, and the memory area is released. The developers have also found a way to store animated GIFs using fewer resources.

Following this and other work, Pavlov comes to the conclusion that Firefox has become substantially leaner than earlier versions and other Web browsers. He says it can stay open longer while using less memory than before. The likelihood of expansions causing memory leaks has also been reduced, he claims. Memory leaks caused by new software can be found quickly, say the developers, because they now have an automated tool for just that purpose.

(trk)