Windows only: Reader David writes in about a user-contributed build of Firefox 3.5 Beta 4 using some custom patches and optimised build settings to make it run faster and use less memory.
Multiple downloads are provided, each one optimised for the processor you are using—most modern PCs can use the P3 build, provided in both regular and portable downloads. The Flash and Windows Media plugins are already pre-installed, and the build uses the new profile-guided optimisation option to speed it up even further. In our brief testing, it definitely feels fast and doesn't appear to use much memory—but since this is a user-contributed build by an unknown (to us, anyway) author and not official you may want to proceed with caution.
Firefox 3.5 Beta 4 optimised Build is a free download, Windows only. If you do try it out, let us know in the comments if you see any speed or memory usage benefits. Thanks, David!