How can I open all Sitecore external general links in a New Browser tab/window by default? And how can I force them to have just a New Browser option when I press Insert External Link.
You need to modify next file :
\Website\sitecore\shell\Applications\Dialogs\ExternalLink\ExternalLink.xml
You have in file :
<Combobox ID="Target" GridPanel.Width="100%" Width="100%" Change="OnListboxChanged">
<ListItem Value="Self" Header="Active browser"/>
<ListItem Value="New" Header="New browser"/>
<ListItem Value="Custom" Header="Custom"/>
</Combobox>
You can delete first and last ListItem from Combobox.
Please copy first time ExternalLink.xml to : \web\sitecore\shell\Override\ folder and after modify file .