I work on an older website that has been functioning for years and after a recent Internet Explorer update we have a iframe based download stop working in IE9-11 most of the time from external networks. It always works fine from our internal network. If we add the site to Trusted Sites it starts working again but that's not going to be a viable solution for our customers.
Would adding a P3P policy to the site correct this issue or is there something else we need to do?
Now this is weird. This is a very old app and apparently sometimes the latter half of the page would take just a little too long to load and IE was firing the domready event before the entire page loaded so the download click handler wasn't able to attach to the bottom controls.
We moved the init from domready to load and added a little more delay and the problem stops happening.