Fix dropping a local charm using Firefox in sandbox mode.
Fix dropping a local charm using Firefox in sandbox mode.

bac/juju-gui,mitechie/juju-gui,bac/juju-gui,jrwren/juju-gui,jrwren/juju-gui,bac/juju-gui,jrwren/juju-gui,bac/juju-gui,mitechie/juju-gui,mitechie/juju-gui,jrwren/juju-gui,mitechie/juju-gui