CPU running at 100%

I was having a problem with the CPU on my iMac running at 99.8 – 100.2 % when Safari (or Firefox) was running (according to the Activity Monitor). To try and resolve this I uninstalled all Safari extensions. I Repaired Disk Permissions. I ran DiskWarrior. I deleted all .plist files from the LaunchAgents folder. I deselected "Show Item Info" for items on the Desktop. None of these solved the problem. What DID solve the problem was this: I removed all the files I had stored on my Desktop. I transferred the files to an external drive. Now the Finder CPU % is at 0.0 at times when it used to be at 100%.