I depend on consistency of my Thunderbird user interface because I use it for a lot of my work and need to be able to use it efficiently. I can appreciate an announcement of a security upgrade, but I don't want to have to change my current user interface every time a new stack overflow is spotted--or at least I could be warned. I turned off automatic update for just this reason. It seems to me that UX thinking ought to include an appreciation of the fact that once a hammer works really well, it doesn't need redesign. I am using Thunderbird right now because it was a much more consistent transition from Netscape years ago.