I'm a consultant using SDL Tridion 2013 at a customers office. (win xp-> now win7, mozilla firefox, always updated, all other components also updated regularly). I have had this trouble quite many years now.
On my laptop Tridion is asking for username/password all the time. When log-in to the system, a pop-up window will come several times.
When clicking any Component, a log-in popup window can come, but not always.
I just updated one news Page, and a log-in pop-up window came about 50 times, luckily it remembers the user-data, so I only need only to press ok/enter.
If I use the system from home, mac os/firefox, I never have these problems. Any idea where I could start to find the solution?