Why adobe flash player slows down all browser's performance?

Question

I rememeber longer ago there were problems with flash player plugin inside Mozilla's Firefox browser causing the plugin to crash: Adobe Flash plugin has crashed - Prevent it from happening again | Firefox Help
After a recent update (17,0,0,134) it almost never crash but it slows down all browsers performance untill it finally launches next video. Almost the majority of all news sites use flash player
to launch its' commercial. And it has several such boxes with commercials, for example: www.lrytas.lt
And while I'm listening to music via youtube and on the other tab reading news on that site, when music clip ends and the browser starts to load other music videoclip,
then the whole browser's work is paralysed - I can't write text, cannot scroll down, cannot click any link. All this is because the system is busy while in youtube next clip is loading.
Mouse marker becomes into round rotating circle indicating loading procedure (firefox is not responding). And it takes time - up to 10-15 seconds to launch new video. Then sudenly all my actions is executed after such pause - my text is typed,
my scroll down  and maybe link is pressed. All this slowing down procedure is annoying. It wastes a lot of time. I open task manager and I see that Firefox is taking 900.000 or 1300.000 K of memory. My OS is Windows 7.
I close whole firefox.exe process and then it automatically close plugins. Then I open the browser again and it ask to automatically recover interrupted sites, I agree with it and then it opens everything again. And again
it is working continuously for some time untill slows down browser again. With more tabs more problems. Moreover, view of a video sometimes comes too late too. Some images are lost as system is too late already because
loading procedure took too much resources.
Long long ago flash player was better. But today with a rise of new ****** substandart computers like iphones ipads you have to evolve the player in such a way that it has to play on everything, but its performance on different platforms
is not the same.
Who is guilty - my PC, Firefox or the plugin? Or maybe I am?
In My Cold Opinion, users actions can't be ignored. The preference should be user's continuous control over a system load.

Answer 1

You are right about high CPU usage. It was even when playing various computer games. I don't have problems anymore. But not because I disabled all addons. I did these things:
In the Location bar, type about:config and press Enter. The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page.
Search for dom.ipc.plugins.flash.disable-protected-mode in the list of preferences.
Double-click on the preference to toggle its value from false to true. (If the setting is already true it means that Flash Protected Mode is currently disabled.)
Close Firefox.
Restart Firefox.
And since then I don't have that particular problem with overloading. I just disabled some of flash protected mode. How is that related with "overloading"? Strage. Hardware acceleration I've enabled again as without it whole text field in news sites is sometimes black.
Thanks anyway Mr.