First of all, why should you even worry about clearing your cache? There are two main reasons:

Reason 1: It frees up space on your computer. After a while, the cache fills up and needs to be cleared so your Web browser will function most efficiently.

Reason 2: It will protect your privacy. This is especially true when several people use the same computer in a workplace or home. If you have privacy concerns, you should regularly clear your cache.

Now, here’s how you can do it:

    1. Open Mozilla Firefox 38.
    2. Click on Tools button and then choose Options.
    3. With the Options window now open, click the Privacy tab on the left side.
Please Note: If using the menu bar, choose Tools and then Clear Recent History. Skip to Step 5 below.
  1. In the History area, click the clear your recent history link.
  2. In the Clear Recent History window, set the Time range to Everything.
  3. In the list at the bottom of the window, check  Cache. (Make sure other boxes are unchecked)
  4. Click Clear Now button.
 That’s all there is to clearing the Cache.