Testrail link: https://testrail.stage.mozaws.net/index.php?/cases/view/76204 Steps: 1. Click on the checkbox in front of Top Sites. 2. Click on the checkbox for "Show two rows". Expected results: Step 1: Checkbox is unchecked. Top Sites are removed from A-S page. Step 2: The checkbox can't be checked as long as the feature is disabled.

Given that the preferences sidebar is moving to about:preferences, the test should just cover whether the preference triggers updates to the content. Disable of top sites is tested https://searchfox.org/mozilla-central/source/browser/extensions/activity-stream/test/functional/mochitest/browser_as_render.js#14-29