Cannot install add-ons in portrait mode

The popup dialog which asks for permissions is cut-off and only the left part is visible. While the "Cancel" button can still be reached, the button to approve is off screen. Thus, it is impossible to install add-ons.

Is it possible to move the dialog to the left such that it starts on the edge of the screen? Or maybe even maximize the dialog?

maybe relevant: https://github.com/MrOtherGuy/firefox-csshacks/blob/master/chrome/urlbar_popup_full_width.css