What Safari could learn from Firefox
Tabs: Firefox has a great setting where all new windows are opened in Tabs. This is great because after I've been poking around the internet, going from Wikipedia to Flickr and all over the place, I don't have a bunch of open browser windows cascading across my desktop. Cascading should be left for style sheets and Apple should implement automatic Tab opening for new window links in Safari. I should note that I just recently learned that Command-Shift-Arrow will take you from tab to tab without using that mouse. I'm a card carrying member of the Keyboard Is Faster Society (KIFS), so this is great news.
Find: Firefox has a great find feature that opens a status bar at the bottom of the page. The function will start searching and highlighting possible finds as you start typing. This helps because I might only need to type a few letters of what I'm looking for and Firefox has already found what I'm looking for. Also, unlike in Safari, which uses a separate pop-up window that goes away after it has completed one search cycle, Firefox's find feature will stay on the bottom of the browser ready for action until you tell it to go away.
Icon: OK, I know this is a trivial point to bring up, but with Apple being so desisgn conscious and Apple consumers looking for that type of forward edge design, the Firefox (and Thunderbird) logo are just cool. Much cooler than a compass (and a stamp). Although, to Apple's credit, if I were going to design a compass icon, it would probably look like Safari's.
Speed: Alright, lets get down to the most important feature. Of all the browsers in use today, Safari is amongst the slowest, if not the slowest. Firefox on the other hand is immediatly fast righ out the box, but with the aid of FasterFox, it leaves Safari in the proverbial dust.
Extensions: Extensions, and to a lesser extent, Themes, are few and far between for Safari. One of the main draws for the Firefox community is the ability to take a browser and add as many bells and whistles as you want - even Abe Vigodas status. Safari has a few addable features, but nothing to the breadth and depth as Firefox. Apple might want to throw a little money at this problem as those individuals who want to create browser extenions are already doing it for all of the indie-browsers.
This captures some of the main reasons I'm constantly switching back and forth between Safari and Firefox. If I had to pick one browser I would probably pick Firefox for all of the features, customizations and optimizations that are available, but I would mourn the loss of Safari like I would a good friend. Hopefully, the engineers in Cupertino are paying attention to all the million+ downloads of alternative browers and start implementing in-house features that can start to compete.