This is for the user with the thunderbird 52 issue.
I went back by mistake today with shift tab and got on a list of dates and a lot of unknown controls.
Sure enough when I entered addons in thunderbird the lightning calendar addon was still installed, previously tb asked to remove it but didn't this time round.
I uninstalled it from addons manager by going to extentions and selecting lightning and hitting remove.
And after a restart my thunderbird window is normal and not full of unwanted bloat.