How can I move the location of Firefox's cache to another drive to free up space on Cdrive?

You can do this by creating a new hidden preference.

1. Type about:config into the location bar and press enter
2. Accept the warning message that appears, you will be taken to a list of preferences
3. Right-click somewhere in the list and select «New > String»
4. For the name of the preference type browser.cache.disk.parent_directory
5. For its value type the path to where you want to store the cache
6. Next locate the preference browser.cache.disk.enable, it must be set to true, if it is not, double-click on it to change its value.

https://support.mozilla.org/ru/questions/768867