In order to change settings to the 'Automatic cache allowance' you can follow these steps.
Using the 'tools' dropdown menu, or the menu button beside the address bar, select 'Options'. In the options menu, select the 'Advanced' section. Within the 'Advanced' section you will select the 'Network' tab. One option within the network tab will be 'Cached Web Content', place a check in the box that says 'Override Automatic Cache Management'. Once this box is checked you will be able to manually select the amount of space you want to be allotted to your cache.
In the current version of firefox, both Disk and Memory are allotted to the browser cache, meaning that your RAM will be used by default. To check that this is the case in your installation you can access the Firefox Configuration utility by typing "about:config" into your address bar, searching for browser.cache.memory.enabled, and checking that the Value component lists 'True'.
Hello, if you want to use only the amount of RAM, try the next :
set the browser.cache.disk.enable to false
check to verify the browser.cache.memory.enable to true
you have to create the browser.cache.memory.capacity
more analytical :
In the Location bar, type about:config and press Enter. The about:config "This might void your warranty!" warning page may appear.
Click I'll be careful, I promise! to continue to the about:config page.
copy and paste in the search field the next bold browser.cache.disk.enable
double-click on it to make it false
now copy/paste in the search field the next bold browser.cache.memory.enable and verify it is true (otherwise double-click on it to make it true)
now right-click anywhere in the list of preferences and select New > Integer and copy/paste the next bold inside the New Integer value browser.cache.memory.capacity click OK and put the next number -1 click OK, exit firefox and restart it.
If anytime you want to reverse the situation then right-click on the preference and select Reset.