Auto merge of #12547 - jryans:wpt-firefox, r=jgraham

Allow running WPT in Firefox

<!-- Please describe your changes on the following line: -->

When working with WPT tests, I find it convenient to compare the results of different browsers / engines. By installing a few more Python packages, we can easily test against Firefox from a Servo checkout.

As noted in the updated README.md, this change allows you to check WPT tests in Firefox by adding `--product firefox` to the `./mach test-wpt` command.

r? @jgraham

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [x] These changes do not require tests because only the set of test harness packages is changed

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3 files changed, 15 insertions, 2 deletions

diff --git a/python/mach_bootstrap.py b/python/mach_bootstrap.py
index 0b5a31c7459..d63f66492d5 100644
--- a/python/mach_bootstrap.py
+++ b/python/mach_bootstrap.py
@@ -135,6 +135,7 @@ def _activate_virtualenv(topdir):
     requirements_paths = [
         os.path.join("python", "requirements.txt"),
         os.path.join("tests", "wpt", "harness", "requirements.txt"),
+        os.path.join("tests", "wpt", "harness", "requirements_firefox.txt"),
         os.path.join("tests", "wpt", "harness", "requirements_servo.txt"),
     ]
     for req_rel_path in requirements_paths:
diff --git a/tests/wpt/README.md b/tests/wpt/README.md
index e0aa6406c41..76073333c46 100644
--- a/tests/wpt/README.md
+++ b/tests/wpt/README.md
@@ -77,6 +77,18 @@ first adding the following to the system's hosts file:
 and then running `python serve` from `tests/wpt/web-platform-tests`.
 Then navigate Servo to `http://web-platform.test:8000/path/to/test`.
 
+Running the tests in Firefox
+----------------------------
+
+When working with tests, you may want to compare Servo's result with Firefox.
+You can supply `--product firefox` along with the path to a Firefox binary (as
+well as few more odds and ends) to run tests in Firefox from your Servo
+checkout:
+
+    GECKO="$HOME/projects/mozilla/gecko"
+    GECKO_BINS="$GECKO/obj-firefox-release-artifact/dist/Nightly.app/Contents/MacOS"
+    ./mach test-wpt dom --product firefox --binary $GECKO_BINS/firefox --certutil-binary $GECKO_BINS/certutil --prefs-root $GECKO/testing/profiles
+
 Updating test expectations
 ==========================
 
@@ -191,5 +203,4 @@ MANIFEST.json can be regenerated automatically with the mach command `update-man
 
 This is equivalent to running
 
-    ./mach test-wpt --manifest-update SKIP_TESTS 
-
+    ./mach test-wpt --manifest-update SKIP_TESTS
diff --git a/tests/wpt/config.ini b/tests/wpt/config.ini
index abd24963da4..7673f0aab8e 100644
--- a/tests/wpt/config.ini
+++ b/tests/wpt/config.ini
@@ -1,6 +1,7 @@
 [products]
 servo =
 servodriver =
+firefox =
 
 [web-platform-tests]
 remote_url = https://github.com/w3c/web-platform-tests.git