Bug 1587416 - Ensure signon.includeOtherSubdomainsInLookup is true when testing subdomain form fill/autocomplete behavior. r=MattN

Differential Revision: https://phabricator.services.mozilla.com/D48789

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

toolkit/components/passwordmgr/test/mochitest/test_autocomplete_tab_between_fields.html

@@ -104,6 +104,7 @@ const tests = [
 ];
 
 add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({"set": [["signon.includeOtherSubdomainsInLookup", true]]});
   ok(readyPromise, "check promise is available");
   await readyPromise;
 });