I've been using Firefox for the last couple of weeks and finally decided to (seim-)permanantly replace Safari with it as my default browser. With the "GrAppl (Brushed) 1.8" theme is looks quite like Safari as well. In two weeks, Firefox has not crashed on me once, and it seems a bit faster than Safari as well, although not dramatically so.
Safari does crash sometimes but the bigger problem for Safari is resources. It has some horrendous memory leaks in it. Over time, memory usage increases to hundreds of megabytes, CPU usage rises and rises to well over 50% on my dual G5, and everything slows to a crawl. When I quit Safari and relaunch it, memory usage immedately goes back down, CPU usage drops, and everything is snappy again. But it always happens (for quit a few versions now, and on multiple Macs I own). Maybe I notice it more than others because I tend to open and close a lot of tabs, but this should not be happening, period. Firefox does not seem to have this problem.
I do miss a few things from Safari such as the Google search history list, having the site history list accessible in a drop-down menu, having each tab's close button directly on the tab rather than way off to the side, and having a directly-clickable "Reveal in Finder" button on each download item. But so far I'm very happy with Firefox overall.