How to turn off caching on Firefox?

The Web Developer Toolbar has an option to disable caching which makes it very easy to turn it on and off when you need it.

Enter "about:config" into the Firefox address bar and set:

browser.cache.disk.enable = false
browser.cache.memory.enable = false

If developing locally, or using HTML5's new manifest attribute you may have to also set the following in about:config -

browser.cache.offline.enable = false