I haven't heard of EYES before. Firefox might have discovered it in the Windows Registry, or you might have downloaded something once and Firefox remembered it.

What kinds of options are listed in the drop-down on the right side next to EYES. Does that help associate it with a particular program?

You can also check the handlers.json file in the profile folder.

You can use the Scratchpad or the builtin JSON viewer to inspect the file.

• "3-bar" menu button or Tools -> Web Developer
• click the "Pretty Print" button to format the file for readability.

• https://developer.mozilla.org/en/Tools/JSON_viewer