Access to Browser Resources in Extension

So, I want to reference chrome://mozapps/skin/places/defaultFavicon.svg in a browser action popup. However, content security means I can’t load it, and restrictions on policies in manifest.json mean I can’t allow for resources from the chrome: scheme whatsoever. Is my only option to rip the icon and bundle it with my extension? I’d rather not pollute my source tree with files that:

a) might change at some point and defeat half the purpose of using “browser_style” in my manifest (which, frustratingly enough, seems to feature some magic by which chrome://browser/content/extension.css makes it in there, note the scheme there)
b) may or may not be under some entirely different license to the rest of my extension.

What am I meant to do?

The big difference in how browser_styles are loaded is that they are injected from outside the sandbox the extension runs in.

Your best option is likely to indeed include the icon yourself. Note that you’ll have to follow the license of the icon (probably MPLv2).

chrome:// and resource:// URIs are generally not loadable in extension (or web) contexts. There are some files that are explicitly allowed.