The no setting part is not really an option. No matter how simple you want to the browser to be, if you want this to be the one browser for the personal use, you need some settings.
* setting search engine - this should be dead simple to implement and totally should be customized. I don't mind using Google but some people just don't like that.
Actually I don't get why Firefox search engine customization is the way it is. If you want to SE that is not part of Firefox's bundle choices, you have to install add-on. To me, this should be simple to implement. A user click on "manage search engine preference", press "Add", gives a URL of the search engine (e.g. https://google.com) and then OK. Firefox should just take whatever user types into the search bar / address bar (this case needs to know whether the "keyword" is url or not) and just redirect user to http://mysearch-engine.com/?q= / ?query=.
I can even imagine this useful when I want firefox to do code search. Imagine instead of me going to dxr.mozilla.org to find the code I want, now I just need to set the search engine to http://dxr.mozilla.org/mozilla-central/search?= yay!
I can even write an addon that does that right now in probably 30-50 lines of JS right now.
* home page. I think many older Internet users still set a home page.
* Download folders - you still want to expose where to set it because some people prefer to set it somewhere else.
* Bookmarks - if there is no concept of bookmark, how exactly do I find the things I want quickly? Imagine I What really helps users, including me, when I just want a browser.
* security, private, clear cookies - awesome, lightspeed would be super awesome on shared computers
* Big buttons. When I first install Lightspeed I should just be prompted a couple pages with big buttons and bars to set homepage / search engine preference
* When I And personally, a little cuteness like the wireframe in the demo is always welcome.
See these scratch drawing 1 and 2. I am not a designer, so pardon me. I am also trying to do a mobile experience here. In the bookmark case, you can type, you can mouse over / click and expand to see the top 5 in that category.
[1]: http://imgur.com/Bvtrnhi&WjAoic8
[2]: http://imgur.com/Bvtrnhi&WjAoic8#1
And yes, as a developer, Lightspeed is awesome to me.