When using Drupal's Webform module, you may find that the form component tabs are missing when you need to edit form fields. This probably has to do with the tabs visibility in your theme. Since I don't use tabs in my theme and rely on the 'Block Edit' module, I found myself struggling to get to the webform component fields.

A solution to this is simply change the administration theme to Garland and specifically the "Use administration theme for content editing" checkbox. This then uses Garland for your webform page edits (activating all the tabs). You can them switch back to your main theme once you've modified your form fields.