Setting pixel density to be independent from OS settings. Fixes issue 6112

Author: barancev

javascript/firefox-driver/webdriver.json

@@ -22,6 +22,7 @@
  "extensions.logging.enabled": true,
  "extensions.update.enabled": false,
  "extensions.update.notifyUser": false,
+ "layout.css.devPixelsPerPx": "1.0",
  "network.manage-offline-status": false,
  "network.http.phishy-userpass-length": 255,
  "offline-apps.allow_by_default": true,