Well, currently I’m working on my project filesio, a platform for distributing large files via web interface instead of FTP.
One of the core abilities of my application is to provide widgets for third-party sites, allowing my users to include download-links to their files in their own web pages. These widgets are simple iframes that load content from my domain.
However, when implementing my app I struggled with the problem that Microsoft Internet Explorer per default blocks cookies set from within an iframe (of course, all other browsers don’t do this).
Lucklily, I found a really ..hm…interesting solution for this problem: