I have this problem as well. In addition, it sounds like my hard drive continously runs with Firefox started. The only way I can shutdown FF is to do a forced quit. Shouldn't have accepted this update.

UPDATE: After upgrading to 8.0.1 I am down to using 808.6 mb of ram, with one tab open(still no add-on's enabled) as compared to 8.0's 1.92 gb. while this still isn't great (firefox 3 only used 630.4mb with 6 tabs open + 2 add-on's) it is starting to fall back down to the realm of acceptable numbers, I guess. I Throw this update up for discussion of the results. The more people I have numbers to compare with the more I can establish a "baseline normal" for version 8. so far I'm working with the ram usage for 10 similar systems(same os, same firefox, all w/ add-on's disabled & only 1 tab open) If you'd like to add your numbers to my research feel free to post them in a reply.

Also, Since upgrading my hard drive doesn't appear to be constantly spooling up, 8.0.1 is also responding to the quit command now instead of making me force quit. It also seems to have quit crashing my system, I will have to give it a bit more time testing it again before I trust it not to crash, but so far, ok.... not great, but ok.