Then, with multiple CPU cores available, software began to be written to take full advantage of the added capabilities inherent with the added CPU cores. At some point, many resource-intensive programs began to heavily rely on the presence of multi-processor architecture to maintain their speedy performance. While many such programs can still operate on single-processor systems, they tend to run slower or require the use of less resource-expensive features by the user in order to maintain a reasonable speed. Beyond that, having each tab and extension running in its own process provides a browser with resistance to total crashing if one tab or extension crashes by itself. Unfortunately, the use of these extra processes requires much more sharing of attention when/if a single-processor CPU is used, hence it tends to slow down such a system's overall operation. Mozilla apparently has elected up until now to maintain their single-process design (which tends to be more optimized for single CPU systems), but there are reports Mozilla will also eventually be moving to a multi-process browser design in the not-so-distant future.

There is a sometimes-unpleasant reality that as hardware inevitably evolves in capability, software also evolves to where it relies on the advanced hardware. This leaves older systems lacking in the necessary capacity to run newer software as effectively. Unfortunately, it's simply the way things are in the real world.

Mozilla "Firefox" running single cpu

Currently yes but it may change.

i love Opera help me

What exactly is the problem with multiple cpu processes for you? Unless you are running a very old and/or very hardware limited computer, multiple processes will not cause any major issues.

Is there a solution in the latest version of Opera

Nope. And all major browser/softwares will go into multiple (cpu) processes sooner or later.