So the problem was this: Even though Windows Folder and Search options were set to 'Open each folder in the same window', each new folder would open in its own separate window, resulting in having many, many windows open at the same time - so annoying!
Respect to David Moore for the solution here. I tried many different 'fixes' but in the end using David's script worked.
Another irritating, strange issue resolved. Phew! Hope this helps someone else.