7f5ad477_ebug_Preferences___FirebugWiki__UI_Equivalents
[Option] showRulers [Description] Specifies whether to display rulers when hovering the parts of the box model inside the Layout Side Panel [Valid Values] true, false [Default] true [UI Equivalents] 
Layout Side Panel Options Mini Menu->Show Rulers And Guides
Firebug Preferences - FirebugWiki