Dell Optiplex GX 60 Desktop PC

[#1]

I found with firefox 6 that if you let it choose it's own cache size it would tend to use vast amounts of disc (if available), which was never reused.
Managing this giant cache can hit the CPU a bit. 

[#2]

Thats because FF is full of memory leaks.

[#3]

Not apparent - my /home directory has around 75GB free - so FF got as far as using a 750MB cache (and still going) before I cut it down to size.

[#4]

Quote from: Steve

Firefox and Quote /usr/bin/Xorg :0 -br -verbose -auth /var/run/gdm/ seems to be taking 40 odd% each,  Anytime I visit a site.

Do you see the same CPU utilisation from Xorg with other apps - GIMP, for example - or just with Firefox?
If it is just Firefox try using a more lightweight browser such as Midori. If you have the Flash browser plug-in installed try removing it.
Dunno which distro you hsve installed, might be worth trying something lightweight like Bodhi Linux.

[#5]

@Foxy yes I noticed about the FF cache a while ago so always cut that down to 250mb max.
@Waldo I had Linux mint Isadora on It but last night I installed puppy Linux on It, Cant get much lighter than that? Yet the PC was still struggling to cope, I have found a spare CPU and heat sink, I am going to try that at the weekend and see what happens.