Yeah, the problem appears to be that I wasn't directing the browser to the php file via localhost. I think what I did was double click on an html file, which loaded in Firefox, but not via localhost, just from the file location (htdocs). Then, I changed the name of the file that I was trying to load to the php file, and it started the issue with creating the tabs.
If you use Firefox, I think you can duplicate the issue pretty easily, if you're interested...