How to Reduce the Available Memory to Firefox

You can instruct Firefox to use less computer memory for its cache.

The Mozilla Firefox Web browser uses different types of cache memory to speed up operations and improve user experience. Among other objects, Firefox keeps Web objects such as images and email messages in an in-memory cache. If the user takes actions that require Firefox to display those objects again, the browser can retrieve them right away -- without having to bring them again over the network or read them off the local disk. If your computer is already under high memory pressure, you can decrease the size of this Firefox cache to free up memory for other applications.

Instructions

1. Launch Firefox by double-clicking on its desktop icon.

2. Type "about:config" into the location bar in the main Firefox window, then press "Enter." Click on "I'll be careful, I promise!"

3. Type "browser.cache.memory.capacity" (the name of a built-in Firefox property) into the "Filter" text field. Firefox will display the current value of the property in the search result area, under the "Filter" field.

4. Decrease the value of the property if it currently has a value greater than zero; that value is the maximum number of kilobytes that Firefox can use for the in-memory cache. Right-click on the property, select "Modify," type a smaller value than the current one and press "Enter."

5. Assign a value smaller than the default for the property if the property does not contain a number of Kilobytes as value. Determine what the default value is based on the amount of RAM on your computer, as per the following table:

   Physical RAM / Memory Cache (in KB)

   32 MB / 2048

   64 MB / 4096

   128 MB / 6144

   256 MB / 10240

   512 MB / 14336

   1 GB / 18432

   2 GB / 24576

   4 GB / 30720

   8 GB and up / 32768

   If the property currently has value -1, right-click on it, select "Modify," type a smaller value than the row on the table corresponding to your computer, and press "Enter." If the property is not defined, right-click on an empty spot on the search result area, select "New," then select "Integer." Enter "browser.cache.memory.capacity" as the name and a number smaller than the row on the table corresponding to your computer, and press "Enter."

References

• Mozilla: browser.cache.memory.capacity