I find lately that I want to look at/compare multiple folders that are not in the same directory/path, or open a directory and look at all folders contained within except for one or two, etc..
I know you can add folders on top of whatever you're already viewing, but if there are a lot, this can be time consuming. I would like to be able to open up a dialog box, hold the CTRL or SHIFT key down and select multiple folders or groups of folders to open at once.
Is this functionality something that could be easily added?
If not, does anyone have a different way to do what I want to do?
TIA!
The toolbar has a folder symbol with a plus, with that you can add the selected folder.
Also, you can use the ordinary windows explorer, select all the directories you want and then drag&drop them while holding down the Ctrl-key - this then adds all the directories to the already loaded ones.
From Windows Explorer you can also select multiple folders and use the context menu (right-click) Mp3tag launch. No need to drag and drop.
Ha! Thanks guys! 
I know I've dragged music files into my player FROM Mp3tag, but I never thought to drag files TO Mp3tag or use the Context menu with multiple folders... feeling a little dopey now....
Just to clarify, I'm aware of the Toolbar button. That's what I was referring to when I said you could add folders on top of what you're already viewing. The problem with that function is you can only add one folder at a time with it.
Anyway, appreciate the help!