Web browsers such as Mozilla Firefox normally save Web pages you access to the disk in their cache. These cached pages can be opened more quickly in the future because the browser doesn't have to re-download them. By default, browsers don't save encrypted pages accessed over HTTPS to disk for security reasons. The preference that disables this security feature is "Do not save encrypted pages to disk" in Internet Explorer. Firefox has its own option that disables this feature.
Type "About:config" into the address bar near the top of the Mozilla Firefox window and press "Enter."
Click the "I'll Be Careful, I Promise" button on the warning page that appears.
Type "disk_cache_ssl" into the filter box at the top of the page.
Right-click the "browser.cache.disk_cache_ssl" preference that appears in the list and click "Toggle" to enable it.
Encrypted pages often contain sensitive data such as banking, credit card or financial information. Saving them to disk increases the chances that this information could be accessed by an unauthorised user or program. Be careful when using the About:config advanced configuration page; it contains a variety of options that can negatively impact your Firefox configuration.