Kottke says: "Mozilla is a toy built by developers for developers..." An understandable point of view given knowledge of how Mozilla was created.
I have some small pushback, though: Another way to assess the browser's intended audience is to include those users for whom the GUI experience (changing preferences, accessing menus) isn't as primary a consideration (or as big a hindrance) as the general browsing or system environment experience (annoying pop-ups, having lots of windows open thus making the Alt+Tab experience on Windows cumbersome).
To these users Mozilla may represent a step forward in their internet experience, even if it takes them a little longer to hunt for the Open Unrequested Windows option. :)
I know many end users who find nearly every GUI a metaphoric challenge and expect an up front pain for every later-enjoyed feature. (Hi, Dad!) Which, I admit, is a far from ideal defense of a mediocre GUI. I just want to point out that some of these users may not care about the menu jumble and just appreciate the fact that the porn pop-ups are gone. (Hi, Mom!)
And also, I'm a end user, too. While I enjoy the support for standards and the improvement of the application architecture, I don't use Mozilla as my primary browser because of those features. It's the pop-up-killing and the fast-loading-on-Win2K and the tabbed-ad-free browser that makes my daily surf more enjoyable than when using IE6.
However, I may change if IE7 kicks butt. I've been known to be shameless.