That just isn't true (and I worked on Chakra while at Microsoft).
I think you're thinking of J++ (Microsoft's version of Java, not JavaScript). Now JScript (Microsoft's version of ECMAScript) does have some minor differences in the dialect, but that was only because the ECMA standard was at a standstill back then. Mozilla had no problems extending their implementation to match either.
I think you're thinking of J++ (Microsoft's version of Java, not JavaScript). Now JScript (Microsoft's version of ECMAScript) does have some minor differences in the dialect, but that was only because the ECMA standard was at a standstill back then. Mozilla had no problems extending their implementation to match either.