firefox scaling was set to true before `mobile-config-firefox` existed.
In new installations false is the default, so explicitly stating false is
only necessary for upgrades. Since the default was changed in one and a half
years ago in fef3af0d75 when the
package was still in version 4, removing it should not have any impact. If
anybody had an edge installation not upgrade for more than 1.5 years, it would
definitely be wiser to reinstall than to upgrade.
With the new mobile-config-firefox, the window width is small enough
that the window does not need to be scaled. This looks better overall,
and avoids scaling glitches.
