Firefox does it wrong
The first launch of an application is arguably the most important. It’s the first impression; it’s when the user decides if they like your app or not. The app should have an immersive first-run experience, and here’s where Firefox does it wrong.
Once you’ve dragged Firefox to your Applications folder, ejected the disk, and trashed the disk image, you probably want to open the app. You are greeted with this:

An import wizard! How fun. Nice seeing a “Go Back” button, even though this is the first screen and there is no way you can go back. Let’s pretend I choose to import stuff. Then I get:

Oh look, I get to select a home page. Except not really, because there’s only one radio button. Let’s continue, shall we?

Cool, thanks for telling me that the stuff has been imported. All I want to do is browse the web.

Firefox now asks to be set as the default browser. How am I supposed to decide now if I haven’t even tried it out yet? Mozilla should show this dialog after the fifth or tenth launch, with a friendlier message like: “Like Firefox? Set it as your default web browser.” In any case, we dismiss the dialog box.

The user is now ready to browse the web. But wait! As soon as we dismissed the last dialog box, a new notification bar slides down, telling us that Firefox is free and open source. Gee. I bet 99.9999999% of users do not care. Also notice that the default window size is totally wrong: there’s a horizontal scroll bar. Seriously, it doesn’t take much effort to change that default window size.
Contrast this to the first-run experience of Apple’s browser, Safari. The first time you launch Safari, the browser plays a beautifully done animation of an Apple logo and a spinning compass. It then redirects to your Top Sites, a gorgeous grid of webpages that you can click on. There are no dialog boxes to click through and no interruptions.

Guess which browser I want to use?