I came to conclusion that the process called ''Opera Helper (Renderer)'' on Mac OS Activity Monitor viewing is using almost 100% of my Apple MacBook Air 2014's CPU Capacity. When i quit this process, the performance of the browser went back to normal and the operations of the opera browser stayed normal.
I hope this helps someone to figure out why there was this much pressure on cpu at the first place, because i don't want to quit this ''Opera Helper (Renderer)'' process manually every time.
It may be possible that this does not cause a lot of problems to people with more than 2 core CPUs but i still have 2 core cpu with 1.5GHz base clock speed. This can cause many people to not recognise this issue at hand. Therefore i hope someone looks into it.