Its interesting I can get it working in Opera because I've had problems with it accessing certain sites, so much so I gave up on it, till I downloaded the latest version and now it seems to open anything. Good for them.
Somewhere on the firefos add-ins page there's a file to add "Open this page in IE" when you left click on a page. If I ever come across anything that doesn't work I just left click and re-open the page in IE. Seems to be drop down menus that don't have "go" buttons that it gets stuck with.