A Firefox user named Taras Glek came up with a 20-line patch that makes Firefox 4 startup up to twice as fast on Windows systems:
Taras Glek, from bugzilla.mozilla.org, found a way to trick Windows into loading Firefox faster by using a simple patch. From the bugzilla.mozilla.org page via Reddit:
Basic idea is that the sequential flag + bull**** read tricks windows into reading xul in Mb chunks instead of stupid 32k(or smaller) ones. Have to do it this way because there is no fadvise() on Windows(that I know of) A big sequential read cuts down on a lot of seeks.
Many users are reporting faster boot times, with load time cut by 50% on slower drives. If this work-around proves to work for the masses, it may be rolled out in the next version of Firefox. Currently, there are users looking to refine the process to make it even more efficient.