Bug 47374: Deal with false positives

Based on https://github.com/stucox/Modernizr/commit/d7ea4878b862367ad7eef0ed26a9d589c5de576a
it seems that we will have to browser sniff to blacklist WP8

Change-Id: I4e18b23510df67e2e8131d645184673f419830c4
Merge "Bug 47374: Deal with false positives"