the HTML script tag and non-JS content - Firefox

Question

It appears this code will request the file in Chrome and IE but not in Firefox.

Answer 1

Is there a some spec that says browsers should only process JavaScript related mime-types?

See the type attribute:

This attribute gives an advisory hint as to the content type of the content available at the link target address. It allows user agents to opt to use a fallback mechanism rather than fetch the content if they are advised that they will get content in a content type they do not support.

If you want to fetch arbitrary content for use in a script, use XMLHttpRequest.