--- a/taskcluster/docker/image_builder/build-image.sh
+++ b/taskcluster/docker/image_builder/build-image.sh
@@ -20,24 +20,34 @@ test -n "$IMAGE_NAME" || raise_error "IM
 
 # The docker socket is mounted by the taskcluster worker in a way that prevents
 # us changing its permissions to allow the worker user to access it. Create a
 # proxy socket that the worker user can use.
 export DOCKER_SOCKET=/var/run/docker.proxy
 socat UNIX-LISTEN:$DOCKER_SOCKET,fork,group=worker,mode=0775 UNIX-CLIENT:/var/run/docker.sock </dev/null &
 trap "kill $!" EXIT
 
+LOAD_COMMAND=
+if [ -n "$DOCKER_IMAGE_PARENT" ]; then
+    test -n "$DOCKER_IMAGE_PARENT_TASK" || raise_error "DOCKER_IMAGE_PARENT_TASK must be provided."
+    LOAD_COMMAND="\
+      /builds/worker/checkouts/gecko/mach taskcluster-load-image \
+      --task-id \"$DOCKER_IMAGE_PARENT_TASK\" \
+      -t \"$DOCKER_IMAGE_PARENT\" && "
+fi
+
 # Build image
 run-task \
   --vcs-checkout "/builds/worker/checkouts/gecko" \
   --sparse-profile build/sparse-profiles/docker-image \
   -- \
+  sh -x -c "$LOAD_COMMAND \
   /builds/worker/checkouts/gecko/mach taskcluster-build-image \
-  -t "$IMAGE_NAME:$HASH" \
-  "$IMAGE_NAME"
+  -t \"$IMAGE_NAME:$HASH\" \
+  \"$IMAGE_NAME\""
 
 # Create artifact folder (note that this must occur after run-task)
 mkdir -p /builds/worker/workspace/artifacts
 
 # Get image from docker daemon (try up to 10 times)
 # This interacts directly with the docker remote API, see:
 # https://docs.docker.com/engine/reference/api/docker_remote_api_v1.18/
 #

--- a/taskcluster/taskgraph/transforms/docker_image.py
+++ b/taskcluster/taskgraph/transforms/docker_image.py
@@ -2,16 +2,17 @@
 # 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
 
 import os
 import re
 
+from collections import deque
 from taskgraph.transforms.base import TransformSequence
 from taskgraph.transforms.task import _run_task_suffix
 from .. import GECKO
 from taskgraph.util.docker import (
     generate_context_hash,
 )
 from taskgraph.util.cached_tasks import add_optimization
 from taskgraph.util.schema import (
@@ -26,16 +27,19 @@ from voluptuous import (
 DIGEST_RE = re.compile('^[0-9a-f]{64}$')
 
 transforms = TransformSequence()
 
 docker_image_schema = Schema({
     # Name of the docker image.
     Required('name'): basestring,
 
+    # Name of the parent docker image.
+    Optional('parent'): basestring,
+
     # Treeherder symbol.
     Required('symbol'): basestring,
 
     # relative path (from config.path) to the file the docker image was defined
     # in.
     Optional('job-from'): basestring,
 
     # Arguments to use for the Dockerfile.
@@ -54,54 +58,78 @@ docker_image_schema = Schema({
 def validate(config, tasks):
     for task in tasks:
         validate_schema(
             docker_image_schema, task,
             "In docker image {!r}:".format(task.get('name', 'unknown')))
         yield task
 
 
+def order_image_tasks(tasks):
+    """Iterate image tasks in an order where parent images come first."""
+    pending = deque(tasks)
+    emitted = set()
+    while True:
+        try:
+            task = pending.popleft()
+        except IndexError:
+            break
+        parent = task.get('parent')
+        if parent and parent not in emitted:
+            pending.append(task)
+            continue
+        emitted.add(task['name'])
+        yield task
+
+
 @transforms.add
 def fill_template(config, tasks):
     available_packages = {}
     for task in config.kind_dependencies_tasks:
         if task.kind != 'packages':
             continue
         name = task.label.replace('packages-', '')
         for route in task.task.get('routes', []):
             if route.startswith('index.') and '.hash.' in route:
                 # Only keep the hash part of the route.
                 h = route.rsplit('.', 1)[1]
                 assert DIGEST_RE.match(h)
                 available_packages[name] = h
                 break
-    for task in tasks:
+
+    context_hashes = {}
+
+    for task in order_image_tasks(tasks):
         image_name = task.pop('name')
         job_symbol = task.pop('symbol')
         args = task.pop('args', {})
         definition = task.pop('definition', image_name)
         packages = task.pop('packages', [])
+        parent = task.pop('parent', None)
 
         for p in packages:
             if p not in available_packages:
                 raise Exception('Missing package job for {}-{}: {}'.format(
                     config.kind, image_name, p))
 
         # Generating the context hash relies on arguments being set, so we
         # set this now, although it's not the final value (it's a
         # task-reference value, see further below). We add the package routes
         # containing a hash to get the overall docker image hash, so changes
         # to packages will be reflected in the docker image hash.
         args['DOCKER_IMAGE_PACKAGES'] = ' '.join('<{}>'.format(p)
                                                  for p in packages)
+        if parent:
+            args['DOCKER_IMAGE_PARENT'] = '{}:{}'.format(parent, context_hashes[parent])
 
         context_path = os.path.join('taskcluster', 'docker', definition)
         context_hash = generate_context_hash(
             GECKO, context_path, image_name, args)
         digest_data = [context_hash]
+        context_hashes[image_name] = context_hash
 
         description = 'Build the docker image {} for use by dependent tasks'.format(
             image_name)
 
         # Adjust the zstandard compression level based on the execution level.
         # We use faster compression for level 1 because we care more about
         # end-to-end times. We use slower/better compression for other levels
         # because images are read more often and it is worth the trade-off to
@@ -187,16 +215,23 @@ def fill_template(config, tasks):
                 worker['env'][k] = v
 
         if packages:
             deps = taskdesc.setdefault('dependencies', {})
             for p in sorted(packages):
                 deps[p] = 'packages-{}'.format(p)
                 digest_data.append(available_packages[p])
 
+        if parent:
+            deps = taskdesc.setdefault('dependencies', {})
+            deps[parent] = 'build-docker-image-{}'.format(parent)
+            worker['env']['DOCKER_IMAGE_PARENT_TASK'] = {
+                'task-reference': '<{}>'.format(parent)
+            }
+
         if len(digest_data) > 1:
             kwargs = {'digest_data': digest_data}
         else:
             kwargs = {'digest': digest_data[0]}
         add_optimization(
             config, taskdesc,
             cache_type="docker-images.v1",
             cache_name=image_name,