In my experience, such fine-tuning tweaks do not make much of a difference on both capable and non-capable machines.

I've tried all kinds of optimisations in an attempt to make browsing experience bearable on my old single-core netbook. Went through the same process on my multi-core desktop, but just to see if I can get perceivable results. It was interesting, but ultimately a waste of time. Got no significant results in both cases.

After that, I decided not to tinker with about:config for general performance optimisations. As I see it, the best optimisations come with the browser updates, and going through about:config is only sensible when you have an urge to have a temporary fix.

Has anyone had better experience fine-tuning their browser?