design patterns - What is the name of this combined button/popupbutton?

This button is in the new Firefox, but what is the name of it?

Answer

This type of button is usually called a 'Split Button'.

The glossary of the Windows User Experience Interaction Guidelines defines the term 'split button' as:

A bipartite command button that includes a small button with a downward pointing triangle on the rightmost portion of the main button. Users click the triangle to display variations of a command in a drop-down menu. See also: command button. [ http://www.microsoft.com/downloads/en/details.aspx?displaylang=en&FamilyID=e49820cb-954d-45ae-9cb3-1b9e8ea7fe8c ]

MSDN's Ribbon Framework Control Library defines a 'Split Button' as:

The Split Button is a composite control with which the user can select a default value bound to a primary button, or select from a list of mutually exclusive values displayed in a drop-down list bound to a secondary button. [ http://msdn.microsoft.com/en-us/library/dd940505(VS.85).aspx ]