For some odd reason, they did not carry over some toolbar settings from 1.5, specifically, the silly "Go" button returned, even though I had it disabled in the previous version. Most likely, the previous version had it as a separate toolbar item, while now it's part of the URL box. The "Go" button is for people to push instead of hitting "return" after typing in a URL. It makes absolutely no sense to me...how is a green triangle at all intuitive for that?
The new way to disable it is to go to URL about:config, search for "browser.urlbar.hidegobutton" (wow, what an awful name for a boolean) and double click on it to set it to "true". The magnifying glass "Go" button on the search box is strangely not similarly disabled. You can remove the icon by editing your user chrome, but that doesn't let you use the space that has now been freed up. Sometimes i wonder why they hide preferences so deeply. For example, there's still no preference item for favorite search engine, even though mozilla had this long ago; it's hidden in about:config.
Yes, I'm pretty obsessive about screen space. Back in the day, I used to operate my browser without any toolbar or URL bar (just a plain unadorned window), but these days the URL bar definitely needs to always be visible to avoid stupid phishing pages, and tabs are useful for web browsing and often easier to manage than windows. I really appreciate programs which don't waste screen space or have customizable space to remove newbie buttons. Programs back then which I liked for their minimal-screen-space maximum-usability interfaces were Newswatcher and Eudora. I relaxed a bit on this in the late 90s when i was always on 21" monitors, but now that i am on a laptop-sized screen for a good part of the day, I'm again killing off useless screen-space fillers.
Interface-usability-wise, I think computing has probably reached an all-time low, but on the other hand, people have become so accustomed to bad usability of web sites that they can now successfully tolerate all sorts of interface crappiness on their computers.
Firefox 2 (OS X) appears to manage memory somewhat better than 1.5, though it's still rather leaky. For example, you can open a bunch of tabs, browse the web for a few days, close all of the tabs and windows, then find that firefox is using a lot more RAM and swap. Sometimes this is due to badly-written extensions, but they don't deserve all of the blame. My conclusion is that if you do a lot of web browsing, you'll still need to quit and restart firefox occasionally, though sometimes the crashes will conveniently do this for you.
Some folks excuse Firefox for having a few elements of crappiness, because it's free and it's far better than MSIE, but the truth is that Mozilla Corp is quite large (for example, around twice as many employees as You Tube), and rakes in a ton of money--A couple years ago, I estimated that they were making around $1-10 per firefox user per year on search affiliate revenue. Every time you google on Google, Yahoo, Amazon, eBay, etc on the firefox search bar, the value of having that company in the search bar goes up. With around 70 million users, that is $70-700 million per year!