The most demanding animation is the changing of the view from the front of the building to the side view showing the crowd gathered in the front.
Below is a zoomed out view of that scene.
This is the version where all the bricks on a level with the same colour are animated as a single brick (the path descriptions are amalgamated into a single path). One brick has had its colour changed to yellow to illustrate the point.
The current version of Chrome performs this animation smoothly. The previous version of Firefox also performed the view change smoothly. The current version of Firefox (August 2015) has difficulty. Opera jumps from one view to another with no real animation.
All browsers fail to perform the animation smoothly if all the bricks are animated independently.