Bug 1711901: Update PBM tests within toolkit/modules/tests to work with https-first-mode enabled r=timhuang

Differential Revision: https://phabricator.services.mozilla.com/D115491

toolkit/modules/tests/browser/browser_web_channel.js

@@ -575,6 +575,10 @@ function test() {
   waitForExplicitFinish();
 
   (async function() {
+    await SpecialPowers.pushPrefEnv({
+      set: [["dom.security.https_first_pbm", false]],
+    });
+
     for (let testCase of gTests) {
       info("Running: " + testCase.desc);
       await testCase.run();