Marking this WONTFIX since Mozilla has no interest in shipping this feature.
@(In reply to Anne (:annevk) from comment #1) > Marking this WONTFIX since Mozilla has no interest in shipping this feature. Do you have a source for "Mozilla" having no interest in shipping this feature? Considering it's a W3C standard (https://www.w3.org/TR/html-imports/), I think one person unilaterally marking it WONTFIX is a bit preemptive.
See https://hacks.mozilla.org/2015/11/an-update-on-web-components-and-firefox/ and earlier https://hacks.mozilla.org/2014/12/mozilla-and-web-components/. And with regards to "W3C standard". 1) It's just a working draft, not a recommendation, and it's supported by nobody other than Google. 2) Mozilla doesn't implement everything the W3C publishes. Not all of it is good.