This extension limits the number of a specific window type that will be up at any one time. Any window type configured as "Yes" in the options (or those windows not listed in the options) will only be allowed 1 window. You can override this behavior by pressing control while clicking. Any window type configured as "No" in the options will behave as before.

Single Window Options.png

Single scaled.png

Multi scaled.png

ADVANCED:
If you want to edit the default windows that will be allowed multiple versions and aren't in the options, edit this line (several window types are in comments below it for ease of use):

aIgnoredWindowClasses = {"masterindex", "charselect_host", "charselect_client"} -- we always ignore these