S.T.A.R.S.
banned
About 30-50% of CPU usage and just over 1 gB RAM when opening 4 tabs in Firefox at once. Admittedly, I did download a game from Steam at the time.
50% CPU usage is too much for a simple firefox and 1 GB of RAM memory is also too much even with 10 opened tabs.
To me CPU usage is 00 to 02 and RAM usage is around 100 MB to 150 MB maximum with multiple opened tabs (about 12 tabs) and not to mention that my complete hardware is a LOT weaker than yours.And yes the results are ALMOST the same on XP AND Windows 7.On Windows 7 the CPU is around 04 (on XP 00 to 02) and MEM usage around 190 MB (on XP 100 to 150 MB),but it is a very small difference than it is in XP so I do not count that.
In short firefox works perfectly on XP and Windows 7.
However the differences in your case are WAAAAAY BIGGER and considering you have such a stronger hardware than mine almost 15 years old,firefox should fly to you and instead it barely works.And as you said the SAME thing also happens with other programs and not just firefox.
So do the following:
NOTE: Disconnect the internet LAN cable and do NOT connect it again until I say so!
You should completely erase your entire HDD using let's say KILL DISK and then install Windows 7 again on UNALLOCATED SPACE which will be the only thing you will see there in the list (after erasing entire HDD using KILL DISK).So select that UNALLOCATED SPACE and click NEXT and Windows 7 will automatically create one partition which uses the entire HDD and then install Windows 7 on it.
After that install SP1 and ONLY SP1!
After that completely disable the Windows 7 update function!
After that install the BASIC DRIVERS ONLY in this order:
-chipset driver (if any)
-graphic driver (if any)
-audio driver (if any)
-LAN network driver (if any)
-wireless LAN network driver (if any)
After that install let's say Mozilla Firefox program and once that has been done,open it,go to options and completely disable update function.Exit firefox.
Now connect the internet LAN cable back in the computer and after that try to use the internet using installed firefox.
Let us know how things work now!
Cheers!