The cover preview thumbnails in the dock used to scale according to how much height the dock area occupied but now the thumbnails don't scale anymore

?
a screenshot would help.

As you can see there is a lot of blank space beneath the thumbnails. The thumbs used to automatically scale according to how much room there is left.

I don't remember thumbs being scaled automatically to the browser space. You have to adjust it manually and it works. Grab the slider in lower-right corner of Status Bar and move it.

I'm pretty sure it did scale automatically but thanks for the tip, I hadn't noticed the slider before