At least on linux permissions-popup and notification-popup panels
don't get side=bottom attribute so the open downwards which causes them to
be drawn outside of screen. Fixes#493
Because the toolbox has display: contents, we need to display the background
separately for each toolbars. In addtion, on linux the main-window has
transparent background-color so we need to set toolbar opacity to 1 to
prevent transparent window areas.
When urlbar is open the panel input-container height changes based on
whether or not go-button is shown. Add a pseudo-element at the end which
has uses the same height value as go-button would.
In addition, this patch adds a pref
userchrome.toolbars-below-content.tabs-at-bottom.enabled that can be
used to make tabs as the bottom-most toolbar.
