I´m not sure if I understand you right: Should Ctrl+Tab be used for switching between connections or between Tabs (as you mentioned firefox)?
Connections are higher in the hierarchy and tabs beneath them. Ctrl+Tab is normally used to switch between MDI child windows, so I guess this refers rather to connections than to tabs (as it is used now).
I have no intention of changing the MDI switch keys as they are Windows standard. We need to think of a more common alternative shortcut key to switch between tabs.