It shouldn’t be hard to implement the APIs, the problem would be sourcing the models to sit behind them. You can’t just steal them off Windows or you will have Copyright Problems presumably. I guess you could try and train clones on Windows against the Windows model results?
I remember it as, Firefox was fast enough, but Chrome was shipping a weirdly quick JS engine and trying to convince people to put more stuff into JS because on Chrome that would be feasible. Nowdays if you go out without your turbo-JIT hand-optimized JS engine everyone laughs at you and it’s Chrome’s fault.