From: DeskNow Knowledge Base
http://www.desknow.com/kb/

FireFox loads all the images again every time I launch it. It is slow
http://www.desknow.com/kb/idx/16/091/article/

By default, Mozilla FireFox does not cache to disk images and scripts if you access them via SSL (https).

So every time you close FireFox and open it again, it will load all the images and scripts, slowing down the first time you access the page.

To change this behaviour, open this URL in FireFox:

about:config

and change the property browser.cache.disk_cache_ssl from false to true

 

Please note that some people may consider this a potential security risk, if the images/scripts that you download contain sensitive information. Use with caution.