The currently available context menu API doesn't provide information on which mouse button was clicked. Version 0.5 ( currently in beta - see first post at http://forums.mozillazine.org/viewtopic.php?f=48&t=3038053 ) adds an option (not enabled by default) to 'Bookmark All Tabs' (in current window) by Shift-clicking 'Bookmark Tab Here' from the context menu of a folder. Hope that helps!