XnView Software

I'd like the option or capability for XnView to browse multiple folder directories at once.

It's a pain having to browse one directory at a time

One thing you can do is:

1. Navigate to a "root" folder
2. Select View->Show files in subfolders.

Another approach would be:

1. Visit all the subfolders individually and assign the same named category to all of the images in each one.

2. Show the category tree and select the category you assigned to the images in the folders you wanted to see altogether...