test(firefox): disable BigInt tests for Firefox (#4849)

Juggler doesn't yet support BigInt transferring.

Author: aslushnikov

test/evaluation.spec.js

@@ -35,7 +35,7 @@ module.exports.addTests = function({testRunner, expect}) {
  const result = await page.evaluate(() => 7 * 3);
  expect(result).toBe(21);
  });
- (bigint ? it : xit)('should transfer BigInt', async({page, server}) => {
+ (bigint ? it_fails_ffox : xit)('should transfer BigInt', async({page, server}) => {
  const result = await page.evaluate(a => a, BigInt(42));
  expect(result).toBe(BigInt(42));
  });
@@ -143,7 +143,7 @@ module.exports.addTests = function({testRunner, expect}) {
  expect(result).not.toBe(object);
  expect(result).toEqual(object);
  });
- (bigint ? it : xit)('should return BigInt', async({page, server}) => {
+ (bigint ? it_fails_ffox : xit)('should return BigInt', async({page, server}) => {
  const result = await page.evaluate(() => BigInt(42));
  expect(result).toBe(BigInt(42));
  });