The only downside using this extension is that it does open a separate IE browser window and doesn't run an IE engine inside your Firefox tab like other extensions do.
If you're having issues, make sure you've set up the extension's options:
≡ > Add-ons > Extensions > IE View WE > Options
Path to Internet Explorer = C:\Program Files\Internet Explorer\iexplore.exe
Website to be opened by IE always = http://example.com/*
