In my experience, at least as of last Friday, you have to use a nightly to get a working version of Pentadactyl, while the version of Vimperator up on the Mozilla add-ons site is fine. I'm personally using Vimperator, just b/c I haven't yet had an itch that it doesn't scratch, and I'm not really clear on what Pentadactyl actually does better (because I'm too lazy to figure it out myself and haven't been able to find a current bullet-pointed list that tells me).
For me it's one of the worst things about Chrome; this window currently has ten tabs open and that's at the _very_ low end for me. With Firefox I can see what I've got open no matter how many I've got because of the pop-down list and the scrolling bar, while Chrome just mashes the list into invisibility.
Firefox has improved a lot. 4 is a fantastic piece of software but it isn't quite as polished as Chrome is.
Despite these issues I greatly prefer Firefox over Chrome. Chrome might be more polished but Firefox is (imho) a much more powerful piece of software and at the end of the day I care much more for power than polish.
1: https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...
https://addons.mozilla.org/en-US/firefox/addon/vertical-tabs...
btw... TabCandy is now called Panorama.
The big thing about Firefox is the Addons: FireBug, NoScript, Adblock Plus, and Pentadactyl (was known as Vimperator) all add up to a fantastic experience.
With Firefox 4 I get the fantastic experience with something much closer to Chrome's speed and tab usability. I don't know if I would say Firefox 4 is quite there yet but it is much much closer.