What's going on here takes a bit of unpacking, so since I've wasted ten minutes doing it let me save others a little time
On normal user systems, presumably particularly Windows, it's very common for malware to "hijack" the browser by modifying its internal settings to be more favourable to the bad guys who wrote or paid for the malware. One way to do this was to modify settings related to what happens when you type something that's not a URL.
So Mozilla.org's solution is to remove this config altogether. No config means nothing for hijackers to hijack. They can still override the main search engine preference, but that has a UI so the user could change it back. Do users actually change it back? I'm skeptical, these are users who are allowing bad guys to run arbitrary code on their PC, they are not very sophisticated. But that's something for the Mozilla.org people to bump their heads against.
What you're seeing here is like DRM restricted movies, client security for first person shooters, and that sort of thing. Theoretically it's an unwinnable war, but that doesn't stop people from fighting it and in the process making your life unnecessarily difficult. So that's what is going on here. The "keyworld.URL hack!" extension is a way to return to what you had when nobody was fighting this particular unwinnable war on your PC.