--- a/testing/mozharness/mozharness/mozilla/testing/firefox_ui_tests.py
+++ b/testing/mozharness/mozharness/mozilla/testing/firefox_ui_tests.py
@@ -258,16 +258,17 @@ class FirefoxUITests(TestingMixin, VCSTo
         if self.config.get('code_coverage'):
             env['GCOV_PREFIX'] = self.gcov_dir
             env['JS_CODE_COVERAGE_OUTPUT_DIR'] = self.jsvm_dir
 
         if self.config['allow_software_gl_layers']:
             env['MOZ_LAYERS_ALLOW_SOFTWARE_GL'] = '1'
         if self.config['enable_webrender']:
             env['MOZ_WEBRENDER'] = '1'
+            env['MOZ_ACCELERATED'] = '1'
 
         return_code = self.run_command(cmd,
                                        cwd=dirs['abs_work_dir'],
                                        output_timeout=1000,
                                        output_parser=parser,
                                        env=env)
 
         tbpl_status, log_level = parser.evaluate_parser(return_code)

--- a/testing/mozharness/scripts/desktop_unittest.py
+++ b/testing/mozharness/scripts/desktop_unittest.py
@@ -712,16 +712,17 @@ class DesktopUnittest(TestingMixin, Merc
                 env['RUST_BACKTRACE'] = 'full'
                 if not os.path.isdir(env['MOZ_UPLOAD_DIR']):
                     self.mkdir_p(env['MOZ_UPLOAD_DIR'])
 
                 if self.config['allow_software_gl_layers']:
                     env['MOZ_LAYERS_ALLOW_SOFTWARE_GL'] = '1'
                 if self.config['enable_webrender']:
                     env['MOZ_WEBRENDER'] = '1'
+                    env['MOZ_ACCELERATED'] = '1'
 
                 if self.config['single_stylo_traversal']:
                     env['STYLO_THREADS'] = '1'
                 else:
                     env['STYLO_THREADS'] = '4'
                 if self.config['enable_stylo']:
                     env['STYLO_FORCE_ENABLED'] = '1'
 

--- a/testing/mozharness/scripts/marionette.py
+++ b/testing/mozharness/scripts/marionette.py
@@ -317,16 +317,17 @@ class MarionetteTest(TestingMixin, Mercu
         env['MOZ_UPLOAD_DIR'] = self.query_abs_dirs()['abs_blob_upload_dir']
         env['MINIDUMP_SAVE_PATH'] = self.query_abs_dirs()['abs_blob_upload_dir']
         env['RUST_BACKTRACE'] = 'full'
 
         if self.config['allow_software_gl_layers']:
             env['MOZ_LAYERS_ALLOW_SOFTWARE_GL'] = '1'
         if self.config['enable_webrender']:
             env['MOZ_WEBRENDER'] = '1'
+            env['MOZ_ACCELERATED'] = '1'
 
         if not os.path.isdir(env['MOZ_UPLOAD_DIR']):
             self.mkdir_p(env['MOZ_UPLOAD_DIR'])
         env = self.query_env(partial_env=env)
 
         marionette_parser = self.parser_class(config=self.config,
                                               log_obj=self.log_obj,
                                               error_list=BaseErrorList + HarnessErrorList,

--- a/testing/mozharness/scripts/web_platform_tests.py
+++ b/testing/mozharness/scripts/web_platform_tests.py
@@ -279,16 +279,17 @@ class WebPlatformTest(TestingMixin, Merc
 
         env = {'MINIDUMP_SAVE_PATH': dirs['abs_blob_upload_dir']}
         env['RUST_BACKTRACE'] = 'full'
 
         if self.config['allow_software_gl_layers']:
             env['MOZ_LAYERS_ALLOW_SOFTWARE_GL'] = '1'
         if self.config['enable_webrender']:
             env['MOZ_WEBRENDER'] = '1'
+            env['MOZ_ACCELERATED'] = '1'
         if self.config['headless']:
             env['MOZ_HEADLESS'] = '1'
             env['MOZ_HEADLESS_WIDTH'] = self.config['headless_width']
             env['MOZ_HEADLESS_HEIGHT'] = self.config['headless_height']
 
         if self.config['single_stylo_traversal']:
             env['STYLO_THREADS'] = '1'
         else: