Bug 1578542: Raptor tests with Firefox crashes are not failing. r=perftest-reviewers,sparky

Differential Revision: https://phabricator.services.mozilla.com/D46955

--HG--
extra : moz-landing-system : lando

testing/profiles/raptor/user.js

@@ -15,3 +15,6 @@ user_pref("dom.push.connection.enabled", false);
 user_pref("browser.dom.window.dump.enabled", true);
 user_pref("devtools.console.stdout.chrome", true);
 user_pref("devtools.console.stdout.content", true);
+
+// prevent pages from opening after a crash
+user_pref("browser.sessionstore.resume_from_crash", false);