So overall, Opera seems to be the fastest browser for windows. Firefox is not faster than Internet Explorer, except for scripting, but for standards support, security and features, it is a better choice. However, it is still not as fast as Opera, and Opera also offers a high level of standards support, security and features.
On Linux, Konqueror is the fastest for starting and viewing basic pages on KDE, but as soon as script or images are involved, or you want to use the back or forward buttons, or if you use Gnome, Opera is a faster choice, even though on KDE it will take a few seconds longer to start. Mozilla and Firefox give an overall good performance, but their script, cache handling and image-based page speed still cannot compare with Opera.
On Mac OS X, Opera and Safari are both very fast, with Safari 2 being faster at starting and rendering CSS, but with Opera still being distinguishably faster for rendering tables, scripting and history (especially compared with the much slower Safari 1.2). Camino is fast to start, but then it joins its sisters Mozilla and Firefox further down the list. Neither Mozilla, Firefox nor IE perform very well on Mac, being generally slower than on other operating systems.
On Mac OS 9, no single browser stands out as the fastest. In fact, my condolences to anyone who has to use one of them, they all perform badly.