i typically have my thunderbird window at about 1/2 size of the screen at all times. if i leave my computer and the monitor sleeps, (not pc) when i return and wake the monitor the window is always resized to about as large as it can go on the screen. i always have to grab a corner of the window and shrink it back down. it has been doing this for about a year. running current windows 10. it does this on a 4 pc's i have. all the pc are configured differently with different hardware but all running windows 10. thunderbird is also the only window that will resize like this. no others are affected.