Ribbet is built on Adobe’s Flash Player. The Flash Player keeps track of all your image edits while you’re running Ribbet. This is useful when you want to undo or redo your edits. To make this possible, it may need to use a very small amount of your computer’s space temporarily.
Ribbet does not download anything onto your computer and the temporary Local Storage space needed is incredibly small: 1mb. You are welcome to ignore the notice, but when the Flash Player needs more space to run efficiently it will continue to ask.