This was due to Firefox at the time not implementing web standards that Chrome did.

Uhm, yeah, that's what browsers do. There are somewhere about 150 web standards and some are hard requirement while others are soft. Blink has some implemented that Webkit hasn't but Gecko has and that's true for all three. Same for browsers.

Btw, the one with the most implemented standards is QtWebkit by far. It's still slower tho.