The Huge amount of memory is used in Mozilla Firefox by default. Method 1: Fix Firefox High Memory Usage by Assigning Fixed Memory Cache The backup will help you in future to easily restore your current settings and preferences. Important note:Before following the below-explained hacks, we recommend you to backup your existing Mozilla Firefox profile and experiment in another profile. You can follow any of these methods and find out how fix Firefox using too much memory and CPU resources. There is a total of six useful methods which we are going to share in this Mozilla Firefox speed up tutorial. Method 4: Don’t Remember Download History.