Can anyone tell me whether Mozilla has shifted its stance on not implementing HTML imports (part of the HTML5 Web Components spec)?
As of 2 days ago (June 9, 2015) Mozilla's position on HTML Imports (as currently specified) has not changed. Here is the reference for this, it goes into more details on HTML Imports and discusses various things that are happening in the area:
https://hacks.mozilla.org/2015/06/the-state-of-web-components/
Here is the original announcement blog post about HTML Imports from 12/2014:
https://hacks.mozilla.org/2014/12/mozilla-and-web-components/