RAM?

[WizardStan]

Even with 30+ tabs open on Firefox, on Windows, or Ubuntu, my memory usage never goes much over 250mb... perhaps it helps that I use Adblock, Flashblock, etc, so there's not much more than text and images on the pages.

30 tabs? Amateur.
I've also got 4 gigs of ram. As I understand (and my understanding has been flawed in the past) Firefox will use more ram if you have more ram, so that might explain my particular spike, which would result in lower usage in a lower spec machine.