How to disable cache in Firefox

Type in the address bar about:config and press Enter (promise to be careful, if asked)

Type in the search bar : browser.cache

And look for the preferences :

browser.cache.disk.enable and browser.cache.memory.enable

Change their values to false

Then close and restart Firefox.

Note : It's best not to set "browser.cache.memory.enable" to "false" when you use Private Browsing mode, as this might cause performance issues.