A workflow suggestion: Glyphs are editable while 'Select Sample Text" window is open.
Why do you need the window to stay open? It can be used with keyboard shortcuts and to get to the next sample text, you don’t even need the window to be open (Edit menu > Other > Select Next/Previous Sample String (you can assign shortcuts to those menus in System Preferences)).
To make bigger jumps within a (long) text file.