This was reported by a user in the german camp-firefox forum, and is confirmed by another user and myself. Affected is 36 Release and 39 Nightly, no test with 37 and 38 Requirements: A fresh installation. After the installation, change the standard search engine in Firefox. Then put the Firefox-widget on the homescreen. Start a search with the widget. Result: The search widget does not use the (new) standard search engine, but still Google. After going back to the Firefox preferences, and doing another change of the standard search engine, this change is now also active on the search widget. So it looks like only the first change before starting the widget does not work. That’s why you mostly need a fresh installation to reproduce this.