hopefully last iteration (let's see what the i586 builds are doing :-()

- disable rust usage for everything but x86(-64)
- explicitely add libffi build requirement

- update to Firefox 52.0.1 (boo#1029822)
MFSA 2017-08
CVE-2017-5428: integer overflow in createImageBitmap() (bmo#1348168)

- reenable ALSA support which was removed by default upstream

- update to Firefox 52.0 (boo#1028391)
* requires NSS >= 3.28.3
* Pages containing insecure password fields now display a warning
directly within username and password fields.
* Send and open a tab from one device to another with Sync
* Removed NPAPI support for plugins other than Flash. Silverlight,
Java, Acrobat and the like are no longer supported.
* Removed Battery Status API to reduce fingerprinting of users by
trackers
* MFSA 2017-05
CVE-2017-5400: asm.js JIT-spray bypass of ASLR and DEP
(bmo#1334933)
CVE-2017-5401: Memory Corruption when handling ErrorResult
(bmo#1328861)
CVE-2017-5402: Use-after-free working with events in FontFace
objects (bmo#1334876)
CVE-2017-5403: Use-after-free using addRange to add range to an
incorrect root object (bmo#1340186)
CVE-2017-5404: Use-after-free working with ranges in selections
(bmo#1340138)
CVE-2017-5406: Segmentation fault in Skia with canvas operations