Applications 'Grey Out' and Stop Working - Why?

[zozza]

Now and again I find that various applications e..g Firefox 'grey out' and become unusable for a few seconds or sometimes permanently.

The attachment provides a recent example.

Why does this happen and how can I prevent it if possible?

Thanks.

[pqwoerituytrueiwoq]

in firefox use one or more of these addons
https://addons.mozilla.org/en-US/fir...on/flashblock/
https://addons.mozilla.org/en-US/fir...ddon/noscript/
https://addons.mozilla.org/en-US/fir.../adblock-plus/

lack of available cpu resources is the most common cause

[Crafty Kisses]

Results of

ps -A
top

Can help determine what's using the most resources

[mayagrafix]

lack of available cpu resources is the most common cause

I've noticed this also and assumed problems executing code or whatever. I have a 4 core CPU with 8 gigs of RAM, so how can this happen?