Internet Explorer was originally based on the NCSA Mosaic browser, which had ports for major UNIX platforms.

Indirectly. IE was based on Spyglass Mosaic, which was a licensee of NCSA Mosaic. However, Spyglass had rewritten it to deal with the substantial differences between the Mac, Windows and X11 ports, so even early versions of IE aren't directly descended. Microsoft eventually removed Spyglass' copyright message around IE 7, suggesting no Mosaic code persisted by then.