Here is the config for Shiretoko:
http://distro.ibiblio.org/pub/linux/distributions/tinycorelinux/2.x/tce/src/shiretoko/mozconfigIt is still a hog, though the --enable-jemalloc option was used to hopefully trim memory usage. I took a look at the swiftfox patch that they used on version 3.5r3 and saw that it only changes some default settings like history retention and maximum connections to a server. It didn't look like it had things that would really change performance beyond being optimized for each specific archetecture. I built Shiretoko as i686 to perhaps improve performance; those with i586 or lower would be much better off with another browser choice.
I am definitely in favor of keeping Minefield available as the Firefox 3.0.x choice. I know they say not to use older browsers, but for non critical web surfing it would be nice to keep choices around for those with lower RAM machines. I may give a custom Bon Echo 2.0.0.20 gtk2 build a go to provide the most recent Firefox 2.x.
Choice is of course a good thing, and using an older browser version is taking advantage of the lower resource requirements while understanding the mild security risk it may involve. I heard it once said that practicing security is more important than patching for security. If you do not practice security but keep your system up to date, you may be at more risk than the user of older software releases that uses good security practices.