I'm aware that it is necessary to login separately on Area 51, Stack Exchange sites or Stack Overflow, etc.
I've been absent (from my PC only for about 20 days) and mostly online via my mobile app about three weeks until last Monday week. Since then even if I leave my favorite pages of Stack Exchange, Area 51, etc. open in Firefox I need to login each day (as described above) at windows shut-down.
I wonder whether this is a bug on the Stack Exchange Network or a Firefox related issue.
I hope you could help me out in both cases!
P.S. 1: Now as I tried to check my Firefox version which actually is 48.0.2, and an update (for 49.0) started!
P.S. 2: The sessions that don't work are running on a Windows 7 VM, and I tried the same on an Ubuntu 12.04 (Precise Pangolin) VM and didn't have that issue at all!
P.S. 3: Changing the cookies setting on Firefox and the update didn't make a change on Stack Exchange. I still need to re-login, and on Area 51 it worked. I didn't try on Stack Overflow, etc. so far!