This patch moves fixtures.js to base.fixtures.ts that sits next to tests. All tests get an extra import to get the base fixtures (both types and implementations).
This roll includes firefox upstream roll. A few tests were hard on me,
so they are currently disabled:
- `should work with subframes return 204`
- `should work when subframe issues window.stop()`
Additionally, new firefox changes cookie treatment that affected a
portion of our cookie tests.
References #3215
