Preferences / Location Bar.
"Location Bar" is the new name for the "File Display Border" and toolbars within it. This is the area directly above each file display, usually containing a path field and buttons for navigation.
The option to ignore clicks on the destination Location Bar now only applies to left clicks. Other clicks (e.g. to open context menus or run RMB/MMB actions) now take place immediately, and don't make that side source (unless the action they perform does so inherently).
If the Location Bar's icon is turned on, clicking it now makes that side the source.
Buttons on Location Bar toolbars can now override their text and background colors.
Thumbnail Size sliders on Location Bar toolbars now only affect the side they are attached to, by default. They can be given arguments to override this.