Opera 9.64; What's Bad?

Web browsers nowadays are more secure compared to its previous releases. Obviously, security is the bottleneck for developing web browsers because a lot of banking transactions are made over the world wide web. I encountered some forums asking which is the best browser and the answers varies from one user to the other. One browser discussed in that forum is the Opera browser. I am amazed on the discussions so I immediately downloaded the installer.

Windows Task Manager showing Opera and Firefox's memory footprint and CPU usage on my system.

When I started using this browser (Opera 9.64), it was all fine until I opened six tabs of different pages of facebook.com (I usually open multiple tabs on facebook). The system starts to slow down and I can feel the CPU's fan is vibrating (more work means more power, more power means more heat, more heat means more cooling effect should be done). For less than 20 seconds, it freezes and slows down everything. When I opened the task manager, a 600+ mega bytes of RAM was only allocated for this browser and the process for running this program requires 95% of the CPU power (almost the same as converting an HD video). The firefox's memory and CPU footprint are relatively low while the Opera is staggering.