I blogged about this at length here: http://www.peterbe.com/plog/did-you-mean-this-domain tl;dr; If you make a typo when typing in a domain name (e.g. www.mozilla.og) the error message looks the same as if you're not connected to the Internet. Using the history of visited sites and an Edit distance algorithm I think that error message can be significantly improved.

Another case is when your provider takes over with their own results. For instance, this is what I see sometimes when mistyping in the awesome bar: http://cl.ly/image/1T311E3Y0J3r http://www.dnsrsearch.com/ www.rr.com

(In reply to Holly Habstritt [:Habber] from comment #1) > Another case is when your provider takes over with their own results. For > instance, this is what I see sometimes when mistyping in the awesome bar: > > http://cl.ly/image/1T311E3Y0J3r That's bug 700470.

(In reply to Holly Habstritt [:Habber] from comment #1) > Another case is when your provider takes over with their own results. For > instance, this is what I see sometimes when mistyping in the awesome bar: > > http://cl.ly/image/1T311E3Y0J3r > That's unfortunate but actually unrelated since it's no longer about that error that I mentioned.

Ok. Makes sense. I thought it would be related to the DNS look up failures. Glad there is another bug for it.

See also bug 663027 and bug 479922

Fixing all of these cases piecemeal might lead us to locally awesome choices that as a whole don't work very well. I hope we can be holistic about understanding and formalizing what model we privilege for what happens in the address bar. When things go awry, I hope we can give people good options for getting back on track. As others point out here, naughty practices by DNS providers and domain squatters have led to a situation where 404s are no longer reliable as indicators of mistyping. Some things that "should" 404 don't (as Holly points out). The awesomebar 'guess what the user means' current implementation isn't transparent, and might have some assumptions that need revisiting.

An easy way to improve this in the short term would be to redirect unrecognized domain names to Google search. I filed this awhile ago, actually, in bug 836750