The Zotero word processor plugin for Word for Mac 2008 doesn't offer a toolbar, instead adding a “Zotero” entry to the AppleScript menu (the manuscript icon to the right of the Help menu):

Most menu commands are also available through shortcut keys.

Word for Mac 2008 lacks support for Visual Basic for Applications (VBA), making it impossible to create a toolbar. VBA support was restored in Word for Mac 2011, and the Zotero plugin for Word 2011 and 2016 includes a toolbar (Word 2011) or Zotero tab (Word 2016).