The submitted title was "Mozilla officially killed Firefox OS". Submitters: it's against HN's rules to editorialize titles like that. The site guidelines ask you to use the original title unless it is misleading or linkbait. Making a title more misleading and more linkbait is the opposite of that.

In this case we changed it to what seems to be the most relevant subtitle. That's ok for submitters to do as well. What's not ok is to make up your own sensational language.