Firefox - Reduce CPU usage and Make it Run Faster

Tips to make Firefox run fast:

Windows prefetch

Newer versions of Windows utilize a mechanism to accelerate the boot process. On Windows XP and Vista systems, the operating system must load many individual pieces of files during the boot-up process for the operating system and applications.Windows maintains a record of the pieces that are loaded during the boot process in a folder. Subsequent rebooting can use this trace to identify files that would be more efficient to load entirely at one time, instead of loading individual pieces across multiple reads of the hard disk. This prefetch mechanism can accelerate the overall performance of the computer.

However, the method of deciding which files to load may not be efficient for Firefox and can require significant CPU resources. You may experience faster performance by removing prefetch files on Windows XP or Windows Vista systems. The prefetch files are stored here:
C:\Windows\Prefetch\

Delete any filename beginning with: FIREFOX

There are some things that we can do to reduce Firefox CPU usage, like:

1. Disable the Java plugin, by going to Tools>Options>Content tab> uncheck Enable Java. Most sites do not use Java. So, you end up wasting CPU resources for a plugin(yes, it is sorta plugin) that you do not use.
2. Disable Images by going to Tools>Options>Content tab> uncheck Load Images automatically. It may sound stupid, but many designers go overboard and add several image backgrounds, coupled with post images. Taking out those darn images out of the equation can work, especially on older PCs. Note that this is a last ditch effort, and you should try other methods mentioned here before trying this one.
3. Open fewer tabs. By this, I mean that you should not open more than ~10 tabs. The more tabs you have, the more memory Firefox consumes. Experiment with the number and come up with an optimal number for your PC.
4. Cut down on the number of extensions used. More specifically, try to remove those extensions which access internet to update information for each site(Alexa toolbar, PR tools, StumbleUpon toolbar etc.).