At the Ubuntuforums there is an index of threads on how to get the best performance out of your Ubuntu machine. On a different note, there is also a post about the problems with Firefox in Ubuntu Breezy (5.10)
Mad Penguin has posted a link to the thread at Ubuntuforums
Use InitNG as a replacement for standard Init.
Speed up Firefox
Custom compile a new kernel. You can also use this tutorial.
Make sure DMA is enabled.
Use Prelink to make applications start faster.
Pick the kernel that's right for your processor.
Disable uneeded services from starting.
Use Swiftfox, a faster Firefox for Intel and AMD processors.
Tweak your ext3/reisers filesystem for enhanced performance.
Clean up unnecessary files
Using Firefox in Breezy?
I have been investigating the situation with firefox 1.0.8 in Breezy
given the presence of known security problems in 18.104.22.168 in Dapper
(for which we are planning to deploy 22.214.171.124 from upstream just as
soon as dapper-security is open).
The situation isn't very good, and none of our options look
particularly good. I thought I should report on what I have
discovered so that we discuss and decide what to do.