title: SourceMap or X-SourceMap handling
body: <p>I can't get firefox (or any browser for that matter) to recognize the <code>X-SourceMap</code> header. For my code. The <code>//# SourceMappingURL</code> comment works on the browser side for me, but I can't use it for reasons specific to my system.</p>
  
  <p>I am curious under what conditions the <code>X-SourceMap</code> header is used to set sourcemaps, as I don't seem to be having success. I am thinking this related to how my code is fetched -- that the devtools somehow don't 'realize' that I'm fetching a javascript file for which a sourcemap should be fetched as well. </p>
  
  <p><a href="https://hg.mozilla.org/mozilla-central/rev/5a0161f8a11e" rel="nofollow">https://hg.mozilla.org/mozilla-central/rev/5a0161f8a11e</a> seems to show how this is implemented, but it's unclear to an eye unfamiliar with this codebase how it is determined that an <code>X-SourceMap</code> header is acted upon. </p>