You have to hack registry for IE, or directly add in Netscape.
Registry Locations
Location used by FindMimeFromData to find MIME type and progID from file
extension:
HKEY_CLASSES_ROOT\.***
Location used by FindMimeFromData to find application from progID:
HKEY_CLASSES_ROOT\\shell\open\command
Location used by URL monikers to find CLSIDs from MIME types:
HKEY_CLASSES_ROOT\MIME\Database\Content Type
