In the end, here's the problem - and it's Microsoft's fault. Not ours, not the developers of the YAF application, f*cking Microsoft.
Problem #1: Because all web browsers are created differently, and all handle web pages differently (even though there are standards enacted to keep this bullsh*t from happening), millions of websites use what's called "Browser Sniffing" to determine what web browser you use. Based on that "sniffing", the web site can determine what 'extra features' your web browser supports. Microsoft completely changed the format of that identifier in Explorer 11. Which basically broke every website in the known world that operates using ASP.NET 4.0 and "Sniffing". Ironically, this is the technique they pushed on us years ago when the technology first came out. Now, we're supposed to use "Feature Detection" - which would mean re-developing millions of sites around the world to accommodate this.
Problem #2: Their solution is for us to re-license new server software and upgrade the whole damned operation. -OR- Rewrite the site to use their new 'feature detection'... NEITHER solution are an option here.
Problem #3: Last month, they released a patch to fix this for all Windows Server platforms that support the software we use (ASP.NET 4)... (Of course, the patch fails - I have been working on this since I posted the first reply, and have made absolutely no progress.
In the end - all our hassles come down to Microsoft. Does it make me want to switch platforms and software and environments? No. Not on your life. Our security and stability are way too important to move everything we have off of MS software. Do I think that Microsoft is evil and hates all sys-admins around the world? You bet'chya...
Will I win this war? You bet'chya... I haven't lost one yet around here...