I haven't tryed this,but found on the Internet. Try it:
type about:config into the firefox navigation bar and hit enter
find the browser.cache.disk.parent_directory, if it doesn't exist right click anywhere and select NEW, then STRING. Enter browser.cache.disk.parent_directory in the first popup box and then the location in the 2nd popup box e.g. k:\tempintfiles. If the entry already existed simply right click on it and select MODIFY and enter your new directory path.
Get a bigger HDD? That seems like a better solution to me.
It would be the better solution, but in the meantime... download ATF Cleaner Welcome to the Frontpage - www.atribune.org right click to run as Administrator, then select the Firefox button and click "Empty Selected".
System Manufacturer/Model Number Bruce ... somewhere in his 40's OS Windows 7 Ultimate 32bit SP1 CPU Intel(R) Core(TM)2 Quad CPU @ 2.40GHz, 2400 MHz Motherboard INTEL/D975XBX2 Memory 4 GB Graphics Card ATI Radeon HD 2600 Pro Monitor(s) Displays Samsung SyncMaster 914v Screen Resolution 1280 x 1024
Keyboard Standard PS/2 Keyboard Mouse Microsoft PS/2 Mouse PSU Rocketfish 700 W Case G.Skill Gigabyte Chassis Hard Drives 2/500GB each ... ST3500630AS ATA Device.
One is not connected Internet Speed DSL Antivirus Avira Internet Security Browser IE 9 Other Info ATI HDMI Audio
Firefox temporary internet files folder... problems?