Limit the CPU usage of a certain application in Linux

You can do this by installing cpulimit. You can limit a certain running application either by name or by process ID:

  cpulimit -e firefox -l 30    

This won’t let Firefox go beyond a 30% CPU usage limit.
If you’d rather go by process, you can do it like this:

  cpulimit -p 3493 -l 40  

This will limit process number 3493 to 40% CPU consumption.