Agreed, there are drawbacks, but he said he already has 9 gigs, so once you already have it, the drawbacks are now irrelevant. What I was arguing is that it's not bad behavior for a program to use more RAM if you have more. I'm not saying that is what Firefox is doing, but if you have 9 GB's, hell, Firefox can use a Gig if it will cause performance enhancements. The problem comes with you have a gig and a half and firefox is using a gig.
Additionally, 9 GB of RAM and keeping more things in RAM does not use more power than paging things to/from disk. Accessing memory from RAM is much cheaper (power and CPU wise) than getting it from disk, nullifying that argument.