I have to agree with Wouter regarding Firefox Iceweasel 3's suckyness. It might be a superior product in many fronts (I prefer it overall to its predecesor), but were it not for the usefulness of its many available extensions (most notably Web Developer, which has become an integral part of my everyday life), I'd have jumped ship for basically any other browser.
I'm just... adding an <AOL>ME TOO!</AOL> on Wouter's comments... WTF, just go to about:config...

So... Are you telling me that Firefox (even if it were the original, Mozilla-blessed version) has a warranty? No? Didn't think so... Go to about:license. You will see the very familiar and expected:

7. Disclaimer of warranty
Covered code is provided under this license on an "as is" basis, without warranty of any kind, either expressed or implied, including, without limitation, warranties that the covered code is free of defects (...)

Other than this downright stupid issue (which by and large goes against the regular Free Software culture), my main gripe is the number of active regions in the location-entry boxes - Yes, I can jump straight to the search box with Ctrl-K and to the location bar with Ctrl-L, but if I happen to try to move between them with good ol' Tab, why must it be inconsistent?
What do I mean? Go to the search field, press Tab. As expected, you are in the Location entry. Now, press Shift-Tab. For 5 points, where are you now? Bzzzt, no, you are not back where you began - You are in a stupid button which looks like your favicon giving you the identity information about the page you are looking at.
Having this button is a great idea - but why does it have to sit in the way of my tabulation? Were it because, in an inspired moment, the Firefox interface designers decided that buttons should be keyboard-accessible, I'd be most happy (it is by far my most mouse-intensive application, and I hate that... But it's just a button embedded in what should be a clean text-entry box.
And for that matter, it is not even a consistent button - Shift-tabbing from the search field will not get you to the search engine selector. And no key combination will lead you to the noisy (and also, mutually inconsistent) iconic buttons at the far right of both fields... Which, again, have no reason to be inside a text entry field!
Oh, and I found another pretty little jewel: Go to any site which has a self-signed SSL certificate. Of course, Firefox will go to great lengths to make sure you understand how unsafe is it for you to trust anybody who didn't pay big bucks to Verisign... But this is enough reason for me to send a bug report:

I am connecting through a crypted HTTPS connection. The site is providing identity information - not certified, right, but it does provide something. And the connection is crypted. Firefox/Iceweasel 2 showed me the URL in a light-yellow background showing the connection was secure - Now it just denies penta.debconf.org the right to call itself secure.
(Yes, I am not an interface designer... But it seems neither are they)
[update]Bug filed. Any comments will be welcome in Bugzilla. The bug with the Debconf site (and I do regard it as a bug) is that Iceweasel displays that Your connection to this web site is not encrypted because some of the elements (i.e. the CSS, images..) are sent in the clear - Even though the real information is crypted. Ever heard of data/visualization decoupling?