Thanks. Perhaps I’ll write a plug-in.
I’d also like to let you know the reason I’d like portrait only. Let’s take Meta Discourse as an example. I’m using an iPhone, so I go to meta.discourse.org on Safari and click on 
and then add to home screen. So everything works fine, and this is what it looks like:
However, when I rotate the screen into landscape mode, and then rotate back to portrait mode, this happens (notice the banner becomes cut off, and it doesn’t go back to normal)
