This chrome-only API was intended to assist developer tools in
reporting the authored values for properties that are normalized after
parsing. We are removing it for four reasons:

1) Only color properties were specially handled by this API.
2) Firefox devtools doesn't call this API, and the only known add-on
that does is Firebug, which has a fallback.
3) There are APIs to do CSS lexing in JS, which provides another way
to retrieve authored values.
4) If this API is retained, the transition to Quantum Style aka
"Stylo" would require significant code changes in the Quantum Style
code and would introduce some performance inefficiency.

If you need to return authored values, you can use a mthod similar to
the one used by the Firefox devtools. There are two chrome-only APIs
in inIDOMUtils.idl:

1) getCSSLexer returns a CSS lexer that will lex some text. The lexer
is documented here:
2) getRelativeRuleLine returns the line number of a CSS rule, relative
to the <style> element that contains it.  This can be useful to find
the proper starting location to extract the text of a rule.

If we proceed with unshipping, Firefox 57 will be the first release
version affected.

Feedback welcome, thank you,

Brad Werth
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