I fail to understand why this phrase is offending you so badly.

  Let’s look at a more interesting example. The current design of 
  mozilla.org is a responsive design. I want to see how the headings 
  will show up on a smaller screen. If I’ve been working on the page, I 
  would likely know some of the IDs and structure used in the page, so 
  I could enter a command like:

"Responsive design" is a fairly established noun in the web design world. This is an article about new developer features in a web browser. Inside the context of the sentence, it's obvious they're talking about how a web page is constructed.

This is how web devs use "responsive design". It's being used by a web dev, in an article for other web devs. You might find it slightly confusing, but that's your problem, not theirs.

OS programmers and corn farmers use the word "kernel" to mean two different things, is this also a crime against nature?