We use Redactor for all of our CMS editors, we love it, flexible, fast, and worked well on mobile. I just encountered an issue that where the editor just wouldn't work with IE11. I spent 1.5 hours trying to figure this out and finally I had to slowly add configurations until I found the one that broke it. Turns out it was running Redactor in an iframe that made IE burp and crap out. Not fun. I had frames on for styling purposes but I turned it off for now. Hopefully this helps someone.