Yes! calc() should work in line-height (and other plain number props) in tomorrow’s @FirefoxNightly, thanks to @MozTW’s Morris Tseng!
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Replying to @heycam
@heycam I think so far it's just line-height and not (yet) other plain number properties, though bugs are filed (1218257, 1258270)

Mar 23, 2016 · 10:19 PM UTC

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Replying to @davidbaron
@davidbaron @heycam line-height's definitely the dumb one, as the sole property in existence that boils down to length+percent+number.
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