when FF is working it make HDD busy too much, never seen such thing in Chrome
hmm... no offense but I see just the contrary here
Firefox is still way too slow at startup, but once it's up and running, it is at least as fast as Chrome. As to extra hard disk activity while browsing, launching a link in a new tab etc... I do see that in Chrome daily, and already reported that on their bug tracker btw. Firefox doesn't have an issue like that and never did. On my system it comes from one thing and nothing else in Chrome: the number of extensions... not one extension in particular, but the number of them. The more loaded, the more swapping to HDD happens when browsing... and strangely this doesn't slow down the browsing.
At the opposite, a big number of extensions will slow down the startup of Firefox (especially on 3.*), but will never affect the browsing behavior (speed, hdd swap).