Edit of dialogs.yml for Opera 12 so the startup dialog gives an option to go in offline mode or online mode to avoid loading every tab. The part that was added is the 2 radio buttons in the last StackLayout. Some reason checkbox does not work (yet), but radios do and good enough.

dialogs.yml

 - type: Dialog
    name: Startup Dialog
    title: D_STARTUP_TITLE
    content:
      type: StackLayout
      name: MainView
      elements:
        - type: StackLayout # pending proper solution, see DSK-343111
          orientation: horizontal
          bottom-margin: 16
          elements:
            - type: Icon
              skin-image: "Startup Dialog"
            - type: Label
              string: D_STARTUP_TITLE
              name: Welcome_label
              font-rel-size: 150
              font-weight: bold
              left-margin: 12
        - type: StackLayout
          minimum-width: 300
          elements:
            - type: Radiobutton
              string: D_STARTUP_LAST_TIME
              name: Continue_lasttime_radio
            - type: Radiobutton
              string: D_STARTUP_SAVED_SESSIONS
              name: Continue_session_radio
              content:
                type: Treeview
                name: Sessions_treeview
                nominal-height: 4c
            - type: Radiobutton
              string: D_STARTUP_WITH_HOMEPAGE
              name: Start_homepage_radio
            - type: Radiobutton
              string: D_STARTUP_WITH_NOPAGE
              name: Start_nowindows_radio
            - type: Checkbox
              string: D_STARTUP_RESTART_EXTENSIONS
              name: restart_gadgets_checkbox
        - type: StackLayout
          minimum-width: 300
          elements:
            - type: Radiobutton
              string: MI_IDM_OFFLINE
              action-string: Work offline
              name: Work offline
            - type: Radiobutton
              string: Work Online
              action-string: Work online
              name: Work online
    button-strip:
      <<: *GenericButtonStrip
      buttons:
        - <<: *OkButton
          string: DI_IDM_START_PREF_BOX
        - *CancelButton
      special-content:
        <<: *DoNotShowAgainCheckBox