I know you would like to see things be the way they used to be as a comfort issue.

However...

BB went through a lot of coding and grief with user feedbacks to get the new library that we are now using. If you will take the time to custiomize it the way you like and actually USE the new features, you will grow to love it.

For instance, the ability to move the material pose files out of the pose area and put them in with the character files (I put them in a folder that shows up under the character files) makes life SO much simpler.

Having the list on the left and the folders on the right seems so natural... I can scan down the text list if I know what I'm looking for, or down the folders (with icons showing!) if I have no idea what the item is called!

It is the most functional Poser library since I started using the program 10 years ago. 

That said, to answer your question:

Open the Klingon toothpick.

Check "Always on top."

Go to Display: Uncheck Tree. Check "Breadcrumbs"

Close the toothpick.

You ought to have something close to what you want.