Good news. In current versions of Firefox there are preferences to control whether Switch to tab entries appear in the urlbar dropdown. Starting with Firefox 36, there is a new UI for these at the bottom of the privacy tab in options. If you uncheck the Opeb Tabs box then you shouldn't need this addon any more.
A new Firefox 4.0 function displays the text "Switch to tab" in the awesome bar dropdown list for any matching pages that are already open in a tab. This is frustrating for some people and difficult to work around if you actually want to open the same page again, cannot be switched off using Firefox preferences, and has several bugs.
This extension completely disables this function. Pages matching your entered text will be opened even if they are already open in a different page or tab.