--disable-installer is ignored since ages (Firefox 14 [1]) and it was Windows
specific.

--enable-gstreamer was removed in Firefox 46 [2].
BuildRequires/Requires/Recommends can be dropped.

--enable-elf-hack is default since Firefox 2 [3] and it enables the feature
depending on platform/architecture [4]. Between Firefox 25 [5] and 36 [6], it
has served to force enable elf-hack, but now it does nothing.

So instead of

%ifnarch ppc ppc64 ppc64le aarch64
ac_add_options --enable-elf-hack
%endif

and

%ifarch %arm
ac_add_options --disable-elf-hack
...
%endif

we can simplify it to

%ifarch ppc ppc64 ppc64le aarch64 %arm
ac_add_options --disable-elf-hack
%endif


[1] https://hg.mozilla.org/releases/mozilla-release/rev/901727f56830

[2] https://hg.mozilla.org/releases/mozilla-release/rev/ca4f31abb4f4
    https://hg.mozilla.org/releases/mozilla-release/rev/5f00c6ec93e9

[3] https://hg.mozilla.org/releases/mozilla-release/rev/9a6de1e28d4b
    https://hg.mozilla.org/releases/mozilla-release/rev/f5d239b735fc
    https://hg.mozilla.org/releases/mozilla-release/rev/aad612e0b8c9
    https://hg.mozilla.org/releases/mozilla-release/rev/850094d1651e

[4]
https://hg.mozilla.org/releases/mozilla-release/file/FIREFOX_46_0_1_RELEASE/configure.in#l7346
(46.0.1)

[5] https://hg.mozilla.org/releases/mozilla-release/rev/f138a2a6c329

[6] https://hg.mozilla.org/releases/mozilla-release/rev/f4c764983416