Useless Rated 1 out of 5 stars
This "Add-On" does nothing "more" than switch the value of:
between 2 (multi Window) and 3 (single Window). Have first a look to:
before you install this useless Add-On and manage your setting by yourself in about:config.
Err - that's the whole point, clicking a button/menu option is far more convenient than going into about:config and battling the dragons