Navigate through Extension Manager tabs via Ctrl-(Shift)-Tab

Now that we have three tabs, it's useful to be able to navigate through the tabs via Ctrl-Tab and Ctrl-Shift-Tab.
It's the shortcut used by browsers like Chrome.
Belated question @MarcelGerber @ingorichter: any idea why this doesn't get snarled up by colliding with the global Ctrl-Tab shortcut for navigating between editors?  Is it because we're in a modal dialog here and native menu commands are disabled while a modal is open?  (On Windows at least, the menu items themselves remain enabled though, so I'm surprised that doesn't "eat" the key event).  Have we tested to make sure this works ok with the non-native HTML menu bar, e.g. on Linux?