Bug 1742963: Disable the page thumbs service in tests. r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D132142

browser/components/places/tests/unit/interactions/head_interactions.js

@@ -19,6 +19,7 @@ XPCOMUtils.defineLazyModuleGetters(this, {
 
 // Initialize profile.
 var gProfD = do_get_profile(true);
+Services.prefs.setBoolPref("browser.pagethumbnails.capturing_disabled", true);
 
 // Observer notifications.
 const TOPIC_ADDED = "places-snapshots-added";