As an admin I have to work with http and https sites quite often. Firefox started to put https in front of everything automatically and clearing the cache all the time is not what I wanted to continue. I found a quick workaround that avoids this issue. Open a new tab and enter about:config in the address bar and hit enter. Confirm the warning and the look for browser.urlbar.autoFill and disable it. With this set to false Firefox stopped that annoying behavior for me.