So I ended up using this method, but for a specific purpose. Here's what happens:
When I'm using my code locally (without committing to my server) on my machine, writing HTML and script tags to the iframe has no problem in IE or FF... meaning, the page works as it should.
When I use this same exact code on my server... FF works, but IE does not.
I found out that if I include a script with the src attribute, IE throws a fit, completely freezing the browser. But locally, IE has no problem using the src attribute. It's just, when it's on a server, it goes bananas.
So what I'm doing is, if it's IE, then I'm making an AJAX call to the corresponding included src file, storing the entire file in a variable, and writing that to the iframe. This isn't ideal, and it's only used if the user is using IE, but yeah, it gets the job done.
I'm just curious as to why IE completely denies the src attribute in an iframe if the page is on an actual website vs. it being local... does it just automatically trust local pages? So confused.