[Dev] Let's revert and move changes introduced by bugs #645 and #677 on Iceweasel

[Florian Pelz]

Am I correct in that only Parabola's Iceweasel disables Hello and
upstream does not? Arch generally tries to stay close to upstream.
Parabola may want to do so too because it is what users may expect.

Overriding Iceweasel with a non-Hello Iceweasel in nonprism may or may
not be justified (see discussion about what criterion, …). Overriding it
in libre seems unjustified by the libre criteria IIUC and goes against
some users' wishes and the way it's usually done on Arch. (Unless of
course that Hello smiley icon is non-free as fauno said in the bug tracker.)

Of course using Hello still generally is a bad idea.