"This set of scripts lets you create two new buttons inside Material Editor - which are actually menu items - that allow you to browse back and forth currently selected bitmap inside the same folder without opening File Open Dialog.
For example - you have tons of brick textures and trying to choose which is better. Instead of opening every time File Open Dialog or external viewer you just turn on Show Map in Viewport and begin scrolling bitmaps in current folder starting from currently applied. You can also choose background image pretty same way.
View a screenshot"