I assume you were using the IE Tab add-on for this. Have you checked for add-on updates, in case this has been fixed?

orange Firefox button (or Tools menu) > Add-ons > "gear icon" > Check for Updates

Of course, you may find it simpler to use IE for Windows Updates. Let that churn away in the background (mine used to take forever on Windows XP) and keep doing whatever you're doing in Firefox.

I notice someone posted a review that IE Tab + (one of several similarly named extensions) is not working for them in Firefox 20, either.

https://addons.mozilla.org/en-us/firefox/addon/ie-tab-plus/