chore(firefox): run all tests without "UnhandledPromiseRejection" error

This aligns all Puppeteer tests so that they never throw the
"UnhandledPromiseRejection" when run with Puppeteer-Firefox.

With this patch, the `npm run funit` passes 275 of 460 Puppeteer tests.

References puppeteer#3889.

test/navigation.spec.js

@@ -16,7 +16,7 @@
 
 const utils = require('./utils');
 
-module.exports.addTests = function({testRunner, expect, Errors}) {
+module.exports.addTests = function({testRunner, expect, Errors, FFOX}) {
   const {describe, xdescribe, fdescribe} = testRunner;
   const {it, fit, xit} = testRunner;
   const {beforeAll, beforeEach, afterAll, afterEach} = testRunner;
@@ -71,11 +71,11 @@ module.exports.addTests = function({testRunner, expect, Errors}) {
       const response = await page.goto(server.PREFIX + '/grid.html');
       expect(response.status()).toBe(200);
     });
-    it('should navigate to empty page with networkidle0', async({page, server}) => {
+    (FFOX ? xit : it)('should navigate to empty page with networkidle0', async({page, server}) => {
       const response = await page.goto(server.EMPTY_PAGE, {waitUntil: 'networkidle0'});
       expect(response.status()).toBe(200);
     });
-    it('should navigate to empty page with networkidle2', async({page, server}) => {
+    (FFOX ? xit : it)('should navigate to empty page with networkidle2', async({page, server}) => {
       const response = await page.goto(server.EMPTY_PAGE, {waitUntil: 'networkidle2'});
       expect(response.status()).toBe(200);
     });
@@ -176,7 +176,7 @@ module.exports.addTests = function({testRunner, expect, Errors}) {
       expect(response.ok()).toBe(true);
       expect(response.url()).toBe(server.EMPTY_PAGE);
     });
-    it('should wait for network idle to succeed navigation', async({page, server}) => {
+    (FFOX ? xit : it)('should wait for network idle to succeed navigation', async({page, server}) => {
       let responses = [];
       // Hold on to a bunch of requests without answering.
       server.setRoute('/fetch-request-a.js', (req, res) => responses.push(res));

test/page.spec.js

@@ -918,8 +918,8 @@ module.exports.addTests = function({testRunner, expect, headless, Errors, Device
       const responses = new Map();
       page.on('response', r => responses.set(r.url().split('/').pop(), r));
 
-      await page.goto(server.PREFIX + '/cached/one-style.html', {waitUntil: 'networkidle2'});
-      await page.reload({waitUntil: 'networkidle2'});
+      await page.goto(server.PREFIX + '/cached/one-style.html');
+      await page.reload();
       expect(responses.get('one-style.css').fromCache()).toBe(true);
 
       await page.setCacheEnabled(false);

test/waittask.spec.js

@@ -124,9 +124,12 @@ module.exports.addTests = function({testRunner, expect, product, Errors}) {
     it('should work with strict CSP policy', async({page, server}) => {
       server.setCSP('/empty.html', 'script-src ' + server.PREFIX);
       await page.goto(server.EMPTY_PAGE);
-      const watchdog = page.waitForFunction(() => window.__FOO === 'hit', {polling: 'raf'});
-      await page.evaluate(() => window.__FOO = 'hit');
-      await watchdog;
+      let error = null;
+      await Promise.all([
+        page.waitForFunction(() => window.__FOO === 'hit', {polling: 'raf'}).catch(e => error = e),
+        page.evaluate(() => window.__FOO = 'hit')
+      ]);
+      expect(error).toBe(null);
     });
     it('should throw on bad polling value', async({page, server}) => {
       let error = null;
@@ -222,9 +225,11 @@ module.exports.addTests = function({testRunner, expect, product, Errors}) {
 
     it('should work with removed MutationObserver', async({page, server}) => {
       await page.evaluate(() => delete window.MutationObserver);
-      const waitForSelector = page.waitForSelector('.zombo');
-      await page.setContent(`<div class='zombo'>anything</div>`);
-      expect(await page.evaluate(x => x.textContent, await waitForSelector)).toBe('anything');
+      const [handle] = await Promise.all([
+        page.waitForSelector('.zombo'),
+        page.setContent(`<div class='zombo'>anything</div>`),
+      ]);
+      expect(await page.evaluate(x => x.textContent, handle)).toBe('anything');
     });
 
     it('should resolve promise when node is added', async({page, server}) => {