What drives me mad is typing queries that have a space. Most of the time it'll do the intended search, but sometimes it'll try to go directly to the domain with the space which immediately fails.
I separated the search box not because I want a search box (I really don't want a browser with a "search box" at all) but because I want un-interpreted, un-looked-up URLs. Though the current URL box doesn't seem to actually search implicitly, it's really hard to tell if its suggestions are coming from the search engine or not and it's at least a step back in the wrong direction).
I'd love any suggestions for making the URL box dumber.
The magic entries in about:config are
keyword.enabled - Turning this off will make firefox never search for something you type in the address bar.
browser.fixup.alternate.enabled - Turning this off will make firefox never try to "fix" the url you type in by putting .com on the end of it.