It depends. If I intend to zero in on a specific page and fine-tune details about that part of the story? I may actually limit it to -one- page. But really, I tend to have a tab open to edit items, several to edit other connected pages, usually at least one unrelated page that I was randomly inspired to work with...
And almost always one tab purely to -play- the game as I'm editing it. Why? So I can see the story how the player would with each change I make and to ensure that every path I think of is properly expanded, explored, and completed. It reassures me that the items do, indeed, show up where they need to, work how they're suppose to, and that I left no page unlinked. Besides, I can critique my storyline better if I imagine it from the player's perspective.