It was the wrong approach because gobs of Javascript gives a horrible UX on low-end, first-iPhone-equivalent hardware, but it was approach they wanted because they're so invested in the notion that FirefoxOS would natively implement Web Platform APIs; conversely those platform APIs would become standard Web-(browser) APIs in the future [1].

Sadly, their ideological mission conflicted with the realities of their target market (and in this case, price-point).

[1] https://developer.mozilla.org/en-US/docs/Archive/Firefox_OS/...