Invite All for Mac
Invite All is a Firefox and Google Chrome add-on that enables you to easily invite all your Facebook friends to an event at once.
All you need to do is to click on the "Select All" button that will appear next to the "Save" button in the friend invite window.
Invite All is cross-platform and it works on Mac OS X, Windows and Linux.
NOTE: To install the Invite All extension for Chrome, drag and drop the downloaded .crx file onto the Chrome Extensions window.