I hear you about slowness and lag. Again, why I am on a quest for tweaks and such.
With all of my tweaks applied in the sticky in this forum I achieve page loads from about 6-8 seconds on a 1.0Ghz PowerBook G4. Now that's total time to load the page. Because of modifying ngpantdelay you are actually reading the content of the page load somewhere around two or three seconds. While you're reading the rest of the page is finishing loading.
On an Intel Mac, with these tweaks applied it's even faster.
But the most important point is that CPU thrashing, which is one of the major problems with Mozilla, returns to normal after the page is loaded. Except for connection issues you don't have the CPU pegged while you're reading a page, which contributes to the sluggishness.
As far as ram, I've done the best I can with finding these tweaks and I think it works fairly well.
All of this is maybe not enough for some people (my page loads in T4Fx beat my pages loads in Safari on PowerPC) but again, I'm willing to sacrafice some speed for customization.
If you have not tried the tweaks, I invite you to try them. It's been made easy to do and there are a few people that weren't sure about it that are converts to it now.
[doublepost=1469371524][/doublepost]Oh, I should mention one other thing.
If you can, turn off all instances of smooth scrolling that you find both in preferences and in about:config.
The computer uses CPU to try and make things scroll smoothly. That makes it sluggish and you end up scolling slowly. But it's on by default. Switch it off and you'll get normal scrolling without sluggishness and without the CPU getting hit.