This has been an issue or me for several months, about the time I upgraded to PCLOS 2013 (I'm not pointing any fingers).
Using Firefox, with 6+ plus tabs open simultaneously, most using Flash version 11,2,202,270. Firefox 19.0.
The system interrupts lock up tight. The Num-Loc key will need 500 msecs (or more) to change the led, the mouse pointer will not move smoothly, and sometimes will not change windows, and certainly will not activate anything.
I normally keep System Monitor loaded, Plugin_container will be the culprit stealing the most cycles. By using the Num-lock key and the mouse to shake up the interrupts, after minutes I am able to End-Process Plugin-Container, which kills Flash and will free up the interrupts - I get my system back. Reset (reload) the FF Tabs that were running Flash and I'm back in business until the next time.
Since this problem occurred, I nixed the onboard nVidia and replaced with an PCIe ATI board, eliminating the possibility that the nVidia drivers were the issue and (to some degree) memory as the ATI card has its own memory.
Any ideas, thoughts, suggestions?