Try typing this into a JS Console: var xx = []; xx[30000000]=42; var yy = xx.slice(0);
It took almost a week to track down this problem where FF was taking 13 seconds to startup. We've spent a lot of time working on this and it is always in the cards to support this on all the other browsers. We've fixed tons of bugs and have gotten closer to it working the way it should, and people have spent countless hours staying very late at the office to try and finish a polished FF release before the deadline, and we just didn't make it in time. I spent the past 5 years of my time working on open web stuff.
Any insinuation that this is an attempt to sell Chrome over Firefox is just flat out wrong. This was a "mobile first" designed app, it's not designed to promote browsers of any stripe, it's designed to promote an experience for gmail users. If we really wanted to shit over a platform, why bother with iOS? Firefox has such a large user base, it can't be ignored, just like iOS can't.