If you use Opera as your browser and have enabled automatic updates, you'll soon notice that the animations are now smoother and they have a more responsive feel. Opera, with their latest update, are now using a technology called "Aura" that has the ability to hardware-accelerate the entire browser, including the user interface.
"The team here put a lot of effort into getting Aura to work properly with Opera and the benefits are already paying off. Aura allows for smoother, snappier animations with a more responsive feel. So far, we have only scratched the surface of this technology, and Opera 21’s primary intention was to get Aura working and stable. In the future, you will see further benefits as it allows us to give everything that little extra bit of polish!" Opera's team lead Ruarí Ødegaard said in the official blog post.
Since, Mac software lacks Aura, Opera has achieved similar results using OS X 's Core Animation.
Other features that are included in Opera 21 comprise of a number of fixes relating to compatibility and stability, it now includes the option to display the full URL in the address field, scales screens that use 200% DPI setting in Windows (no more small fonts), and better performance for Mac keyboards when using web apps.