When I read .smi files on ordinary text editors, they come with many tags. But I can read this without tags using Internet Explorer, I think. How can do this on Mac? I tried Safari, Chrome and Firefox but all failed.
I don't know whether the .SMI you have is a Synchronized Accessible Media Interchange (SAMI) file or a Synchronized Multimedia Integration Language (SMIL) file. The latter is used by RealPlayer especially and is an XML-based format, whereas the former is an HTML+CSS based format.
Regardless, if IE is hiding the tags then that's a result of how its parser and layout engine are dealing with the format, and it's unlikely you can replicate this on a Mac. If you're editing the files then a good text editor would be recommended anyway, and hiding the tags makes no sense. If you want to view the files, instead of doing so separately use a media player that'll display them along with their associated videos.