diff --git a/testing/mozharness/mozharness/base/python.py b/testing/mozharness/mozharness/base/python.py
index 745e515b23a0..4801ea804ae9 100644
--- a/testing/mozharness/mozharness/base/python.py
+++ b/testing/mozharness/mozharness/base/python.py
@@ -126,6 +126,7 @@ class VirtualenvMixin(object):
         optional=False,
         two_pass=False,
         editable=False,
+        legacy_resolver=False,
     ):
         """Register a module to be installed with the virtualenv.
 
@@ -136,7 +137,16 @@ class VirtualenvMixin(object):
         applied.
         """
         self._virtualenv_modules.append(
-            (name, url, method, requirements, optional, two_pass, editable)
+            (
+                name,
+                url,
+                method,
+                requirements,
+                optional,
+                two_pass,
+                editable,
+                legacy_resolver,
+            )
         )
 
     def query_virtualenv_path(self):
@@ -250,6 +260,7 @@ class VirtualenvMixin(object):
         global_options=[],
         no_deps=False,
         editable=False,
+        legacy_resolver=False,
     ):
         """
         Install module via pip.
@@ -280,6 +291,8 @@ class VirtualenvMixin(object):
                 command = [pip, "install"]
             if no_deps:
                 command += ["--no-deps"]
+            if legacy_resolver:
+                command += ["--use-deprecated=legacy-resolver"]
             # To avoid timeouts with our pypi server, increase default timeout:
             # https://bugzilla.mozilla.org/show_bug.cgi?id=1007230#c802
             command += ["--timeout", str(c.get("pip_timeout", 120))]
@@ -505,6 +518,7 @@ class VirtualenvMixin(object):
             optional,
             two_pass,
             editable,
+            legacy_resolver,
         ) in self._virtualenv_modules:
             if two_pass:
                 self.install_module(
@@ -515,6 +529,7 @@ class VirtualenvMixin(object):
                     optional=optional,
                     no_deps=True,
                     editable=editable,
+                    legacy_resolver=legacy_resolver,
                 )
             self.install_module(
                 module=module,
@@ -523,6 +538,7 @@ class VirtualenvMixin(object):
                 requirements=requirements or (),
                 optional=optional,
                 editable=editable,
+                legacy_resolver=legacy_resolver,
             )
 
         self.info("Done creating virtualenv %s." % venv_path)
diff --git a/testing/mozharness/scripts/awsy_script.py b/testing/mozharness/scripts/awsy_script.py
index 9c5a4519aa4d..288c17aae107 100644
--- a/testing/mozharness/scripts/awsy_script.py
+++ b/testing/mozharness/scripts/awsy_script.py
@@ -163,14 +163,14 @@ class AWSY(TestingMixin, MercurialScript, TooltoolMixin, CodeCoverageMixin):
 
     @PreScriptAction("create-virtualenv")
     def _pre_create_virtualenv(self, action):
-        requirements_files = [
-            os.path.join(self.testdir, "config", "marionette_requirements.txt")
-        ]
+        requirements_file = os.path.join(
+            self.testdir, "config", "marionette_requirements.txt"
+        )
 
-        for requirements_file in requirements_files:
-            self.register_virtualenv_module(
-                requirements=[requirements_file], two_pass=True
-            )
+        # marionette_requirements.txt must use the legacy resolver until bug 1684969 is resolved.
+        self.register_virtualenv_module(
+            requirements=[requirements_file], two_pass=True, legacy_resolver=True
+        )
 
         self.register_virtualenv_module("awsy", self.awsy_path)
 
diff --git a/testing/mozharness/scripts/desktop_unittest.py b/testing/mozharness/scripts/desktop_unittest.py
index 8ea2aa532852..35416f2f3a5f 100755
--- a/testing/mozharness/scripts/desktop_unittest.py
+++ b/testing/mozharness/scripts/desktop_unittest.py
@@ -430,12 +430,17 @@ class DesktopUnittest(TestingMixin, MercurialScript, MozbaseMixin, CodeCoverageM
         self.register_virtualenv_module(name="mock")
         self.register_virtualenv_module(name="simplejson")
 
-        requirements_files = [
-            os.path.join(
-                dirs["abs_test_install_dir"], "config", "marionette_requirements.txt"
-            )
-        ]
+        marionette_requirements_file = os.path.join(
+            dirs["abs_test_install_dir"], "config", "marionette_requirements.txt"
+        )
+        # marionette_requirements.txt must use the legacy resolver until bug 1684969 is resolved.
+        self.register_virtualenv_module(
+            requirements=[marionette_requirements_file],
+            two_pass=True,
+            legacy_resolver=True,
+        )
 
+        requirements_files = []
         if self._query_specified_suites("mochitest") is not None:
             # mochitest is the only thing that needs this
             if PY2:
diff --git a/testing/mozharness/scripts/marionette.py b/testing/mozharness/scripts/marionette.py
index aceebb0648bd..9524983d1d33 100755
--- a/testing/mozharness/scripts/marionette.py
+++ b/testing/mozharness/scripts/marionette.py
@@ -269,7 +269,10 @@ class MarionetteTest(TestingMixin, MercurialScript, TransferMixin, CodeCoverageM
                 "Could not find marionette requirements file: {}".format(requirements)
             )
 
-        self.register_virtualenv_module(requirements=[requirements], two_pass=True)
+        # marionette_requirements.txt must use the legacy resolver until bug 1684969 is resolved.
+        self.register_virtualenv_module(
+            requirements=[requirements], two_pass=True, legacy_resolver=True
+        )
 
     def _get_test_suite(self, is_emulator):
         """
diff --git a/testing/mozharness/scripts/web_platform_tests.py b/testing/mozharness/scripts/web_platform_tests.py
index 70fd0e932895..d0fcf54c046c 100755
--- a/testing/mozharness/scripts/web_platform_tests.py
+++ b/testing/mozharness/scripts/web_platform_tests.py
@@ -259,7 +259,10 @@ class WebPlatformTest(TestingMixin, MercurialScript, CodeCoverageMixin, AndroidM
             dirs["abs_test_install_dir"], "config", "marionette_requirements.txt"
         )
 
-        self.register_virtualenv_module(requirements=[requirements], two_pass=True)
+        # marionette_requirements.txt must use the legacy resolver until bug 1684969 is resolved.
+        self.register_virtualenv_module(
+            requirements=[requirements], two_pass=True, legacy_resolver=True
+        )
 
     def _query_geckodriver(self):
         path = None