Let’s start with the results for the browsers on my Windows XP SP2 installation, ordered from slowest to fastest. Each test was executed 2 times, clicking on the results will teleport you to the detailed results where you can paste the URL’s of another test to compare.
The MSIE7-results are probably not entirely representative, as I use Tredosoft’s standalone IE7. This is a bit of a hack to have IE7 on my otherwise MSIE6-based system. Moreover my corporate Windows-installation is infested with crapware, notably McAfee OAS and Zonealarm seem to be slowing things down enormously. The codinghorror-tests indeed show significantly better results for this browser, although IE does have serious issues with string concatenation, which should be fixed in IE8.
On the same hardware, but booting in Ubuntu 8.04 (Linux) form my external USB HD (a.k.a. my ‘disktop‘), I got the following results:
Firefox 3 RC1 seems slightly slower then b5, but maybe the Ubuntu-b5-version is compiled with optimizations? Firefox is also faster on Ubuntu, but the anti-virus-bloat is probably messing with our heads here (although Opera is slower on Linux, go figure).