Allow custom handling of DNS failures
I like to be able to type search keywords straight into the location bar. Without a proxy, Firefox's "keyword.URL" feature lets me do this. If there's just a single word and it's potentially a hostname, Firefox will first try to treat it as one, almost always getting a DNS failure before submitting it using keyword.URL. When there's a proxy configured it doesn't make sense for Firefox to attempt to detect DNS "host not found" errors -- it might have no access -- so it just hands a request for http://foobar/ to the proxy and returns what the proxy does.
I'd like you to consider including this patch.