Tools/complements (or addons, I don't know in Englis version of FF). Look for IETab and hit uninstall.
But I'm pretty sure that isn't causing anu problem. As long as you dont have any IE Tab open in FF it isn't even loaded.

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>On the other hand, I haven't resolved FireFox problem. I think I now wish to un-install IE extension, but I'm not sure how to do it.