Resizing panes and browsers

Most panes are surrounded by a border or divider that can be dragged to resize the pane in question. Some borders appear when the cursor moves over them, but are hidden otherwise to eliminate unnecessary clutter. 

(shown here as red lines)

Click and drag to resize. Some have minimum width/height that will trigger a panel auto-collapse (for example files list is useless if you can see just icon and 5 letters of the name, so it collapses to 0 when you release mouse button)

Many borders or dividers have Drag Handles (the double dotted lines) and Open/Close Arrows:

Collapsing a Browser to create a single-browser layout

For dual-pane layouts. Each Browser has a minimum width (Standard Layout) or height (Columns Layout). When that minimum is reached a "collapse" message appears, and if the Left Mouse Button is released the Browser in question collapses. It can be restored by clicking on the Open/Close Arrow that points in the "open" direction, or by dragging the Drag Handle.