User Agent: Mozilla/5.0 (Windows NT 6.1; rv:50.0) Gecko/20100101 Firefox/50.0 Build ID: 20100101 Steps to reproduce: Open a new tab with activity stream addon. Actual results: With the default sandbox level of 3, I get the following page: https://0x0.st/dOw.png In the console I get the following error: > A coding exception was thrown and uncaught in a Task. > > Full message: ReferenceError: PreviewProvider is not defined >Full stack: getScreenshot@resource://gre/modules/commonjs/toolkit/loader.js -> resource://activity->streams/addon/lib/getScreenshot.js:31:5 _getLinks/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://activity-streams/addon/Feeds/TopSitesFeed.js:130:30 >TaskImpl_run@resource://gre/modules/Task.jsm:331:42 With sandbox level 2, nothing changes but with level 1 the error is same but I get the following page: https://0x0.st/dO4.png where the activity stream is stuck loading. Expected results: Activity stream should load as expected.