diff --git a/taskcluster/ci/test/kind.yml b/taskcluster/ci/test/kind.yml
index c47ef11c3..7ae17da14 100644
--- a/taskcluster/ci/test/kind.yml
+++ b/taskcluster/ci/test/kind.yml
@@ -5,11 +5,16 @@
 loader: taskgraph.loader.transform:loader
 
 transforms:
+    - fenix_taskgraph.transforms.test:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 job-defaults:
-    description: Test Reference Browser
+    description: Test Fenix
+    include-pull-request-number: false
+    run:
+        using: gradlew
+        use-caches: false
     treeherder:
         kind: test
         tier: 2
@@ -17,9 +22,6 @@ job-defaults:
     worker:
         docker-image: {in-tree: base}
         max-run-time: 7200
-    run:
-        using: gradlew
-        use-caches: false
 
 jobs:
     debug:
@@ -43,9 +45,7 @@ jobs:
         attributes:
             build-type: debug
             code-review: true
-        treeherder:
-            symbol: ui
-            platform: 'ui-test/opt'
+        include-pull-request-number: true
         run-on-tasks-for: [github-pull-request, github-push]
         run:
             # TODO Generate APKs in a build task instead
@@ -57,6 +57,9 @@ jobs:
                   key: firebaseToken
                   path: .firebase_token.json
                   json: true
+        treeherder:
+            symbol: ui
+            platform: 'ui-test/opt'
         worker:
             docker-image: {in-tree: ui-tests}
             env:
diff --git a/taskcluster/fenix_taskgraph/__init__.py b/taskcluster/fenix_taskgraph/__init__.py
index 3023bc278..e0e516166 100644
--- a/taskcluster/fenix_taskgraph/__init__.py
+++ b/taskcluster/fenix_taskgraph/__init__.py
@@ -9,7 +9,7 @@ import re
 
 from importlib import import_module
 from six import text_type
-from voluptuous import Required
+from voluptuous import All, Any, Range, Required
 
 from taskgraph.parameters import extend_parameters_schema
 
@@ -25,6 +25,7 @@ def register(graph_config):
     _import_modules(["job", "worker_types", "routes", "target_tasks"])
     extend_parameters_schema({
         Required("head_tag"): text_type,
+        Required("pull_request_number"): Any(All(int, Range(min=1)), None),
         Required("release_type"): text_type,
         Required("release_version"): text_type,
     })
@@ -41,6 +42,9 @@ def get_decision_parameters(graph_config, parameters):
     parameters["release_type"] = _resolve_release_type(head_tag)
     parameters["release_version"] = head_tag[1:] if head_tag else ""
 
+    pr_number = os.environ.get("MOBILE_PULL_REQUEST_NUMBER", None)
+    parameters["pull_request_number"] = None if pr_number is None else int(pr_number)
+
     if parameters["tasks_for"] == "github-release":
         for param_name in ("release_type", "release_version"):
             if not parameters[param_name]:
diff --git a/taskcluster/fenix_taskgraph/transforms/test.py b/taskcluster/fenix_taskgraph/transforms/test.py
new file mode 100644
index 000000000..bbf7b8f2d
--- /dev/null
+++ b/taskcluster/fenix_taskgraph/transforms/test.py
@@ -0,0 +1,20 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import absolute_import, print_function, unicode_literals
+
+from taskgraph.transforms.base import TransformSequence
+
+
+transforms = TransformSequence()
+
+
+@transforms.add
+def add_pr_number(config, tasks):
+    for task in tasks:
+        include_pr = task.pop("include-pull-request-number")
+        if include_pr and config.params["pull_request_number"]:
+            task["worker"]["env"]["PULL_REQUEST_NUMBER"] = str(config.params["pull_request_number"])
+
+        yield task