diff -up mozilla-esr31/browser/confvars.sh.webm-fix mozilla-esr31/browser/confvars.sh
--- mozilla-esr31/browser/confvars.sh.webm-fix	2014-07-21 13:56:53.522253529 +0200
+++ mozilla-esr31/browser/confvars.sh	2014-07-21 13:57:49.983533186 +0200
@@ -65,6 +65,6 @@ MOZ_PAY=1
 # Enable activities. These are used for FxOS developers currently.
 MOZ_ACTIVITIES=1
 MOZ_JSDOWNLOADS=1
-MOZ_WEBM_ENCODER=1
+#MOZ_WEBM_ENCODER=1
 # Enable exact rooting on desktop.
 JSGC_USE_EXACT_ROOTING=1