File Extension IE3 File Format Internet Explorer 3 file IE3 stands for Internet Explorer 3 file. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question I'm On The Train... Follow Up to How Much Bandwidth How does the UK move to a high resilience, secure and ubiquitous, post-internet, any-to-any "mesh"?