Theme Appears Differently in Different Browsers

I did a theme update as well as a couple plugin updates on my site as well as a client’s site. It looks great in Firefox but is totally a mess in IE. I deactivated the plugins to see if that was the source of the problem but nothing changed. I’ve since reactivated them. I’ve checked settings and even deleted a reinstalled the theme. HELP! This is just crazy! What am I missing?

My site is https://www.real-estate-support.com.

I know someone much smarter than me has the answer. Appreciate it!

~Pamela