Chiming in with a simple example:

Two finger pinch zooming on a Macbook stutters enormously in Firefox and is much smoother on Chrome.

I use this feature all the time and it's made switching to Firefox difficult.

Another example:

I'm not a fan at all of how Firefox handles displaying huge amounts of tabs. Tiny arrows to scroll your tabs left and right is really a disorienting nuisance and I much prefer Chrome's system of making tabs smaller. I'm sure there's a way to change this, but I'd rather stay on the default path that they're actively iterating on and improving.