Does what it says it would. My only gripe is that it seems to merge everything into whichever window has the most tabs open rather than whichever window you actually clicked on the button in. But that is a minor annoyance.

When I click the button, it merge the current windows to another one. Illogical.

When I click on the extension, it minimizes firefox if one of the tabs in another window was minimized.

C x