Work Around!
Simply copy the frame/main/main.html to a file named frame/main/index.htm . Once you've done that, you can have the copied file launch automatically, and when the pages are redirected by links, they'll still go to the original page. You can also use META code to automatically redirect immediately.
The key here is to remember that you need to do the copy every time you update the main page.
Also, see if the software you're using will allow you to change the name of the file at the entry point. My Ancestry software allows me to change the initial page to anything I want.