Enable Web Inspector in Safari v 8.0 in Yosemite OS
defaults write NSGlobalDomain WebKitDeveloperExtras -bool true

adds Inspect Element to the right-click menu

However, opening the Develop menu will do it too

defaults write com.apple.Safari IncludeDevelopMenu -bool true

One additional note about toggling the Develop menu this way is that it isn't interactive with the Safari prefs pane, &amp; can result in reversed behaviour if later toggled from there by the user.