Cold fusion is new concept within science, it's never been proven to work or be possible (my laymens interpretation). Whereas humans being able to decipher the Firefox code base, as per the example, is no more than an extremely complex set of 'calculations' and functions in our brain - which, with enough time and resources, can be replicated by a computer or sorts.

One is an idea for which there is no ground to base it on, the other is an existing thing which can be recreated. Quite the difference.