firefoxWrapper: switch to GStreamer 1.0

wkennington@f6c1004 switched Firefox to GStreamer 1.0 by changing its
buildInput *only*, but that is not enough. We need to fix Firefox
wrappers by changing their buildInputs and set GST_PLUGIN_SYSTEM_PATH_1_0
instead of GST_PLUGIN_SYSTEM_PATH.

With above changes playing H.264/MP4 media works in firefoxWrapper and
conkerorWrapper as tested with
http://www.quirksmode.org/html5/tests/video.html and
https://soundcloud.com/immclovin33/synthetix-sundays-53-with-marko-maric-19715



It should help with peti#9247

Reviewed-by: kmicu <kmicu@protonmail.ch>
Tested-by: kmicu <kmicu@protonmail.ch>