I noticed that firefox has been tracking more history than I thought I'd asked it to, so went to use the 'Clear History' option. I selected 'Everything' but then deselected 'Cache' 'Active Logins' and 'Site Preferences' - specifically because I didn't want to have to log back into everything that I keep logged in - forums, social media etc, as I can't always remember my passwords, and my computer is only used by me. Unfortunately when I re-opened Firefox, all such sites were logged out - and I'm just not sure why?