Here's a small online tool to convert/view images from/to the IFF format:
http://tool.anides.de
The tool runs completely on your machine in your browser so there's no communication with a server at all.
Use drag and drop or click on the background to load the image(s). Choose "Save" to download the converted IFF image.
Please note that a recent version of Firefox or Chrome is recommended and also that the IFF support is not complete.
Here's an example screenshot of the website.
Sascha