A hard one to describe, but I'll try.
In windows, when file Explorer is opened you get the little search box at top right which allows you to type in partial file names, keywords, etc. (filters filenames)
In Photoshop CC when you open you get the same filename search box top right.
However when I open a file in CS5 I get no search box. No way to filter filenames.
I'm wondering if there is something I did or if there is a way to get that search / filter box when opening a file in CS5.