In the next week millions of people will begin upgrading to Firefox 4. A large number of them will be upgrading from Firefox 3 so they'll be disappointed to learn that when you type a name or phrase into the Awesome Bar it no longer takes you directly to the website you are looking for. Technically this feature was called Browse By Name but most people probably understand it as performing a "feeling lucky" search in Google. The forums and support site are already filling up with complaints.
If you were just here trying to fix it then you can go now, the rest is a rant...
In Firefox, all UI changes are hotly debated by a passionate community of users. I was pretty passionate about this feature and I'm sad to see it go because it made Firefox stand out as a superior web browser. Many people will encounter the new default behavior in Firefox 4 and will not think that there is a solution and may never find this web page.
The arguments for disabling this feature were pretty weak. People were worried that the feeling lucky search was unpredictable and slow. In my experience, it works 99% of the time which is more than good enough. If I ever want to get raw search results then I type cmd+K to use the search bar. As for slow, it does add a couple milliseconds but you don't actually need the feeling lucky search for most searches because they will be in your history; the Awesome Bar will autocomplete them for you. Thus, it is not slow in practice, it is just there when you need it.
It's nice not to think about URLs but rather to think about web pages as topics or ideas. This fits well with my brain and that's how I want to navigate the web. As the search engine quickly became our main entry point into the web, the web was able to transform into a big blob of ideas and information. Your thoughts and questions are indeed reflected in web pages; IP addresses and named URLs are just technical details that you don't need to care much about.
UPDATE: Per comments, I forgot to mention that another major argument from the UX team was that Browse By Name violated the least surprise and consistent result principles by being non-deterministic (type something and one of 3 things can happen). But rules are made to be broken and in this case I would argue to make a compromise since the feature works 99% of the time. Without it, I feel quite crippled actually.
UPDATE: The LuckyBar addon does in fact use the Browse By Name service, not exactly the Feeling Luck search. The key difference is that Browse By Name will not redirect to a random site if the term is ambiguous, which is what you want. I actually didn't know the Feeling Lucky button worked differently because I haven't used it since 1996.
UPDATE: As I predicted, a mere 24hrs after the Firefox 4 release and this is a frequently reported issue on the Firefox Support site.