I right clicked and it opened it back up in Internet Explorer not Firefox. When I do right click the only option I have is "Open Link Target in IE" Maybe that ad-on didn't really work?
The add on works for me. Now try this, if the IE tab is listed in the Add-Ons under tools......
Right click on one of the icons in the Navigation Toolbar (The part of firefox that has the back, forward, home, etc buttons), click on Customize.
Drag the IE tab icon onto the toolbar. Now go to the webpage in question normally as you do. Then click the IE Tab icon that you should now see in the Navigation Toolbar so that webpage is reloaded using the IE Tab.
In that image above, do you see the new tab next to the home tab? That's the icon I am referring to above, and when you click it, you should see the firefox icon like shown above to show that you have switched into the IE tab's IE mode.