If all goes according to plan, the browser should be available before the end of the year. It’s been in development for a year and a half.
What will Fennec do to convince you to try it out, much less switch to it full-time (provided you have a Nokia N900, of course)? There’s a clever syncing feature that ensures whatever you view on your desktop version of Firefox will be available on the mobile version. That is, if I’m reading the Wikipedia entry on, say, WrestleMania 10 on my desktop, that same Web page will be displayed when I launch the mobile version of the browser. Handy, yes.
Fennec will have tabbed browsing. The AwesomeBar also makes an appearance.
And yes, there will be Add-Ons. Whether that means you’ll be able to load up Adblock Plus (don’t leave home without it!) and Scriptmonkey and so forth isn’t exactly clear. Maybe you’ll need mobile-specific Add-Ons?
As for that iPhone version jab: since when did Apple approve Apps that replicate “core functionality” of the iPhone? (Mobile Safari says hi.) Your best bet is to hope someone is able to get the code up and running on Apple’s little device, then releases a binary on one of those Jailbroken App repositories.