Firefox hung on me a few minutes ago. That's not a problem, right? Sure, there was a time when you'd lose your work in every application when one crashed. But nowadays, we have secure multiuser operating systems. We have private memory and preemptive multitasking and nobody loses all their work when one program crashes. That battle was won long ago. Right?
Right. When Firefox hung, I lost my work in several applications, because those applications were web-based, and the same browser held them all. Modern computer usage - mine and many people's - is so browser-heavy that a crashing browser is nearly as bad as a crashing system. It just reboots faster.
I didn't actually lose everything. Only Firefox's graphics thread hung, so I was still able to switch to the tab with my unfinished email, blindly select the text, and copy it to safety. Preemptive multitasking saved me, but in a different place than where it was intended to. There's a lesson about unexpected utility here...
I still lost my navigation state: the twenty or so tabs that told me what I was reading and doing. (The number of tabs tells you something about my browsing style.) This is reconstructible from history, but it's jarring to lose it - it breaks my trust that things stay where I put them. This sort of state goes a long way toward making users feel comfortable with a machine. As usual, comfort was the biggest casualty of the crash. Unreliable tools are usually easy to deal with, but their mental cost can far exceed the small amount of time they waste.