Version:           4.7 (using KDE 4.7.2) 
OS:                Linux

Just the ability to resize the folder by resizing, or if not possible with qt then a dock similar to kdevelop.  

Also the ability to hide it completely

Reproducible: Always

Steps to Reproduce:
Try to resize to not visible

Actual Results:  
stops at minimum width/height

Expected Results:  
resizes to show just the outer edges

This is an effort to bypass the use of the folder list.

Saw this in Mac's recent mail app.  That is just a search and a list, I want folders and since the tabs are so conveniently located.  

In thunderbird I had the view pane right, the list to the left of that, the folder view collapsed to the left of that (just in case). Then tabs to display the folders.