Re: keyword.URL stopped not working for single words, goes to 'website-unavailable.com' instead
You may have an ISP that automatically redirects you to a search page if a DNS look up fails.
That takes the control from Firefox to do the normal keyword search like a Google I'm Lucky search.
In such cases you need to contact your ISP and ask for a DNS server to opt-out of that feature.
You can also check if there is a link on the search results page to go to your ISP and opt-out.