One thing most people complaining against Firefox is its startup time. It requires lot of time to load during startup. You can notice this if you have multiple browsers installed on your computer. However, now that is a past story. Mozilla is implementing a new technique in Firefox 7 to double the startup speed. Firefox 7 is currently in beta and the final version will be released on Sep last.
What does Firefox to reduce the load time? Basically, Firefox tells the OS to forcefully preload a library (xul.dll/libxul.so/XUL library) before passing it on to the runtime linker. Though, this patch was proposed to use in Firefox 4, it is now implementing in Firefox 7.
However, one problem that makes it nearly impossible to use faster startup time in Windows OS, according to the developer of this patch, is Windows Prefetch. He says, “Optimization only works when prefetch is disabled/broken”. That is, Firefox should be faster with Windows Prefetch off.
However, there is a workaround that one may get Windows Prefetch to not slow down Firefox startup. Here it is.
“Above helps populate the Windows Prefetch in a less counter-productive way. On warm startup Windows Prefetch records irrelevant IO operations and blocks Firefox startup to preload files that Firefox accesses after startup”.
Another issue, according to him is, less than 25% of Windows users have Windows Prefetch off and can benefit from vastly improved Firefox 7 startup. The remaining (above 75%) users therefore may not get benefit from faster Firefox 7 startup because of those issues.
You can read more about this topic at Mozilla website.