How to allow middle-clicks to close last tab on Firefox 3.5?

A middle-click on a tab will close a tab on Firefox except for the last tab. I know that there is some setting somewhere that allows this because I have one PC set up long ago which does this, and one PC which I set up recently which doesn't.

Closing the last tab causes it to turn into a blank page.

Does anyone know how to switch this setting on?

Solution 1:

See this article : "Closing the last tab in Firefox 3.5" for how to manually do this.
The article also recommends this add-on : Last Tab Close Button, which quote "shows Close button on the last tab in Firefox 3.5*, which closes the last tab but not the browser".

Solution 2:

Try using TabMixPlus. Among other things, it can set this behavior to what you want. It also has a lot o other nice features that you might like.