Back in 1994 when web browsers were new, we expected a little instability. Hell the operating systems on which they ran were pretty damn flaky too. When Netscape came out, we all justified the flakiness to ourselves by marvelling at the great new features: things like tables and blink tags.
Now explain to me why web browsers are still flaky? I don't use Internet Explorer if I can help it, but the RSS viewer I use at work does have it embedded. At least twice a day, the IE component flakes out, taking all the "seen" data with is.
As my main browser, both at home under Linux and at work under Windows, I use Mozilla Firebird. It's a great browser in most respects fast, standards compliant and massively configurable. The one regard where you see its Netscape lineage is stability. It hangs, eats progressively more memory the longer it's open and the Linux version regularly sits there chewing 100% CPU while seemingly doing nothing.
Now I'm willing to give the developers the benefit of the doubt. They rely on a bunch of plug-in developers' code for stability, and I suspect the Macromedia Flash and Java plugins might well be problematic. But it's nearly ten years since 1994 when the web explosion happened, and you'd kinda expect some progress in that time...