browseForDoc only for PDFs?

I'm trying to automate some page generation. Some of the pages need to be generated from TIFF files. The directories from which these TIFFs come are consistent enough for a person to follow them...but not for a computer(sometimes people append information to the end of individual part directory names). I can do this manually by going to Document - Insert Pages - From File, and it lets me select from all sorts of wonderful file types. But when this line runs in my script:

var insrtpath = app.browseForDoc({bSave: false, cFilenameInit: "*.tiff",cFSInit: ""});

I'm only allowed to pick from PDF documents. The drop down box at the bottom doesn't let me pick anything else. I stuck the *.tiff in these in hopes that it would help and Acrobat steam rolled right over it and changed it to .pdf. Changing it to .tiff manually in the box doesn't help.

Does browseForDoc only work for PDFs? Am I missing some top secret parameter? Is there another method that can provide similar functionality(I've been looking to no avail)?

Even if I have to forgo this portion and do it manually, it won't be the end of the world. Nowhere near as important as my stamps hiding underneath button icons thread(Which you should really go look at. It's fun for the whole family, I promise)