PDFs opening in extra-wide window in Skim 1.6.6
https://sourceforge.net/projects/skim-app/files/Skim/Skim-1.4.36/
Indeed, I confirm the bug as well (on Mojave). It renders Skim unusable for me, and I had to downgrade to 1.4.36 to restore sanity. Looking forward to the next release!