Mozilla User Experience Designer Alex Faaborg describes the new visual experience in Firefox 3 and attempts to answer some criticisms of the design. I don't feel he's adequately addressed the concerns, which I'll outline again below within the context of the final Firefox 3 look and feel:

The overall goal of the Firefox 3 visual refresh was visually integrating with the platform, while still maintaining a unique identity and presence by using the keyhole form for the navigation controls.

Keyholes

The one exception to this cross platform visual identity was Linux, where we decided against using the keyhole form in favor of uplifting the native OS theme’s navigation controls. On many Linux distributions we are often already the default browser, so there is less of a need for us to establish a visual presence, and it makes more sense to seamlessly integrate with the rest of the desktop environment.

So I'm going to call BS on this one. Mozilla wants to "visually integrate" with the underlying platform while maintaining "a unqiue (Firefox) identity." And yet, they only visually integrate with Linux and only maintain their unique identity on non-Linux platforms. No offense, guys. But this is both inconsistent and contrary to your supposed goals. Visually integrating with the underlying OS makes sense. You should do it for your volume users as well as the Linux minority.

And speaking of the "keyhole" navigation buttons, if this is such a good idea, why not use this control in the Library window? Witness these pointlessly different Back and Forward buttons:

Here's the excuse for this travesty:

On OS X the Library window is reminiscent of the Finder, and on Vista the window has a similar visual style as other media collection applications, like Windows Media Player and Windows Photo Gallery.

Except that it doesn't. There's a black bar, as in WMP, yes, but the navigational buttons are different in the shot above. Why are they different from both WMP and from the main Firefox window? Again, it's inconsistent, and for no good reason.

Moving along...

Did We Achieve Our Goal for this Visual Refresh?
Firefox 3 is way ahead of Firefox 2 when it comes to visual integration with the desktop environment on Linux. From using native gtk widgets in the content area to uplifting the OS theme icons, we have made an incredible amount of progress with this release.

In terms of overall visual integration, I believe on XP we clearly met this goal. Firefox 3 visually integrates with XP by using the platform’s color palette while tweaking the style enough to still appear modern on an aging OS.

On Vista we do a great job visually integrating with icons and with our set of secondary windows, although the main window is notably missing support for Aero glass. Users will hopefully be able to get this functionality using an extension during the life cycle of Firefox 3, and we will have glass support added to XUL for the next release of Firefox.

Ah, so even Mozilla admits they did not actually achieve their goals for this visual refresh on Windows Vista. That's refreshing (pardon the pun), but it does nothing to address the inconsistency issues. If you're going to be inconsistent with the underlying OS, at least be consistently inconsistent. (If that makes sense.)

Now look at this mess:

If you didn't know better, you'd assume those two windows were from two different applications. But they're not. You've got two different toolbar types (color scheme/icon sets), different navigational controls, completely different visual styles.

Put simply, Firefox 3 is a user interface disaster on Windows Vista and doesn't satisfy the promises Mozilla made last year, sorry. (And before someone points out that the Library window in that post closely matches the Library window shown above, well duh. The issue is that the entire Firefox UI doesn't match that look and feel, something that would indeed allow the browser to closely integrate with the look and feel of Vista.)