--- a/accessible/tests/mochitest/elm/a11y.ini
+++ b/accessible/tests/mochitest/elm/a11y.ini
@@ -9,10 +9,10 @@ skip-if = buildapp == 'mulet'
 [test_figure.html]
 [test_listbox.xul]
 [test_MathMLSpec.html]
 [test_nsApplicationAcc.html]
 [test_plugin.html]
 skip-if = buildapp == 'mulet'
 [test_canvas.html]
 [test_shadowroot.html]
-skip-if = stylo # bug 1293844
+skip-if = !stylo
 support-files = test_shadowroot_subframe.html

--- a/accessible/tests/mochitest/treeupdate/a11y.ini
+++ b/accessible/tests/mochitest/treeupdate/a11y.ini
@@ -10,16 +10,17 @@ support-files =
 [test_bug883708.xhtml]
 [test_bug884251.xhtml]
 [test_bug895082.html]
 [test_bug1040735.html]
 [test_bug1100602.html]
 [test_bug1175913.html]
 [test_bug1189277.html]
 [test_bug1276857.html]
+skip-if = !stylo
 support-files = test_bug1276857_subframe.html
 [test_canvas.html]
 [test_colorpicker.xul]
 [test_contextmenu.xul]
 [test_cssoverflow.html]
 [test_deck.xul]
 [test_doc.html]
 [test_gencontent.html]

--- a/devtools/client/inspector/markup/test/browser.ini
+++ b/devtools/client/inspector/markup/test/browser.ini
@@ -83,17 +83,17 @@ skip-if = os == "mac" # Full keyboard na
 [browser_markup_accessibility_new_selection.js]
 [browser_markup_accessibility_navigation_after_edit.js]
 skip-if = os == "mac" # Full keyboard navigation on OSX only works if Full Keyboard Access setting is set to All Control in System Keyboard Preferences
 [browser_markup_accessibility_semantics.js]
 [browser_markup_anonymous_01.js]
 [browser_markup_anonymous_02.js]
 skip-if = e10s # scratchpad.xul is not loading in e10s window
 [browser_markup_anonymous_03.js]
-skip-if = stylo # Stylo doesn't support shadow DOM yet, bug 1293844
+skip-if = !stylo
 [browser_markup_anonymous_04.js]
 [browser_markup_copy_image_data.js]
 subsuite = clipboard
 skip-if = (os == 'linux' && bits == 32 && debug) # bug 1328915, disable linux32 debug devtools for timeouts
 [browser_markup_css_completion_style_attribute_01.js]
 [browser_markup_css_completion_style_attribute_02.js]
 [browser_markup_css_completion_style_attribute_03.js]
 [browser_markup_display_node_01.js]

--- a/devtools/server/tests/mochitest/chrome.ini
+++ b/devtools/server/tests/mochitest/chrome.ini
@@ -46,16 +46,17 @@ support-files =
 [test_framerate_02.html]
 [test_framerate_03.html]
 [test_framerate_04.html]
 [test_framerate_05.html]
 [test_framerate_06.html]
 [test_getProcess.html]
 [test_highlighter_paused_debugger.html]
 [test_inspector-anonymous.html]
+skip-if = !stylo # No shadow dom support
 [test_inspector-changeattrs.html]
 [test_inspector-changevalue.html]
 [test_inspector-dead-nodes.html]
 [test_inspector-display-type.html]
 [test_inspector-duplicate-node.html]
 [test_inspector_getImageData.html]
 [test_inspector_getImageDataFromURL.html]
 [test_inspector_getImageData-wait-for-load.html]

--- a/dom/base/test/mochitest.ini
+++ b/dom/base/test/mochitest.ini
@@ -571,19 +571,19 @@ skip-if = toolkit == 'android' #bug 6870
 [test_bug922681.html]
 [test_bug927196.html]
 [test_bug962251.html]
 [test_bug976673.html]
 [test_bug982153.html]
 [test_bug999456.html]
 [test_bug1022229.html]
 [test_bug1025933.html]
-skip-if = stylo # bug 1293844
+skip-if = !stylo
 [test_bug1037687.html]
-skip-if = stylo # bug 1293844
+skip-if = !stylo
 support-files = test_bug1037687_subframe.html
 [test_bug1043106.html]
 [test_bug1057176.html]
 [test_bug1060938.html]
 [test_bug1064481.html]
 [test_bug1070015.html]
 [test_bug1075702.html]
 [test_bug1091883.html]
@@ -610,16 +610,17 @@ skip-if = toolkit == 'android'
 [test_bug1318303.html]
 [test_bug1375050.html]
 [test_bug1381710.html]
 [test_bug1384661.html]
 [test_bug1399605.html]
 [test_bug1404385.html]
 [test_bug1406102.html]
 [test_bug1421568.html]
+skip-if = !stylo
 [test_caretPositionFromPoint.html]
 [test_change_policy.html]
 [test_clearTimeoutIntervalNoArg.html]
 [test_constructor-assignment.html]
 [test_constructor.html]
 [test_copyimage.html]
 subsuite = clipboard
 skip-if = toolkit == 'android' #bug 904183

--- a/dom/events/test/mochitest.ini
+++ b/dom/events/test/mochitest.ini
@@ -134,24 +134,24 @@ skip-if = (e10s && os == "mac") || webre
 [test_bug1003432.html]
 support-files = test_bug1003432.js
 [test_bug1013412.html]
 [test_bug1017086_disable.html]
 support-files = bug1017086_inner.html
 [test_bug1017086_enable.html]
 support-files = bug1017086_inner.html
 [test_bug1079236.html]
-skip-if = stylo # bug 1293844
+skip-if = !stylo
 [test_bug1145910.html]
-skip-if = stylo # bug 1293844
+skip-if = !stylo
 [test_bug1150308.html]
 skip-if = true || stylo # bug 1293844, bug  1421545
 [test_bug1248459.html]
 [test_bug1264380.html]
-run-if = (e10s && os != "win" && !stylo) # Bug 1270043, crash at windows platforms; Bug1264380 comment 20, nsDragService::InvokeDragSessionImpl behaves differently among platform implementations in non-e10s mode which prevents us to check the validity of nsIDragService::getCurrentSession() consistently via synthesize mouse clicks in non-e10s mode. bug 1293844 for stylo.
+run-if = (e10s && os != "win" && stylo) # Bug 1270043, crash at windows platforms; Bug1264380 comment 20, nsDragService::InvokeDragSessionImpl behaves differently among platform implementations in non-e10s mode which prevents us to check the validity of nsIDragService::getCurrentSession() consistently via synthesize mouse clicks in non-e10s mode.
 [test_bug1327798.html]
 subsuite = clipboard
 [test_clickevent_on_input.html]
 skip-if = toolkit == 'android' #CRASH_DUMP, RANDOM
 [test_continuous_wheel_events.html]
 [test_dblclick_explicit_original_target.html]
 [test_dom_activate_event.html]
 [test_dom_keyboard_event.html]

--- a/dom/html/test/mochitest.ini
+++ b/dom/html/test/mochitest.ini
@@ -435,17 +435,17 @@ support-files =
 [test_formData.html]
 [test_formSubmission.html]
 skip-if = toolkit == 'android' #TIMED_OUT
 [test_formSubmission2.html]
 skip-if = toolkit == 'android'
 [test_formelements.html]
 [test_fullscreen-api.html]
 tags = fullscreen
-skip-if = toolkit == 'android'
+skip-if = toolkit == 'android' || !stylo
 support-files =
   file_fullscreen-api.html
   file_fullscreen-backdrop.html
   file_fullscreen-denied-inner.html
   file_fullscreen-denied.html
   file_fullscreen-esc-exit-inner.html
   file_fullscreen-esc-exit.html
   file_fullscreen-hidden.html

--- a/dom/tests/mochitest/webcomponents/mochitest.ini
+++ b/dom/tests/mochitest/webcomponents/mochitest.ini
@@ -1,9 +1,10 @@
 [DEFAULT]
+skip-if = !stylo
 support-files =
   inert_style.css
   dummy_page.html
   head.js
 
 [test_bug900724.html]
 [test_bug1017896.html]
 [test_bug1276240.html]
@@ -36,11 +37,10 @@ support-files =
 [test_template.html]
 [test_template_xhtml.html]
 [test_shadowroot.html]
 [test_shadowroot_clonenode.html]
 [test_shadowroot_inert_element.html]
 [test_shadowroot_style.html]
 [test_shadowroot_style_order.html]
 [test_style_fallback_content.html]
-skip-if = stylo # Bug 1410170
 [test_link_prefetch.html]
 [test_bug1269155.html]

--- a/layout/reftests/bugs/reftest.list
+++ b/layout/reftests/bugs/reftest.list
@@ -1859,17 +1859,17 @@ pref(layout.css.moz-document.content.ena
 == 1053035-1-grid.html 1053035-1-ref.html
 == 1059167-1.html 1059167-1-ref.html
 == 1059498-1.html 1059498-1-ref.html
 == 1059498-2.html 1059498-1-ref.html
 == 1059498-3.html 1059498-1-ref.html
 == 1062108-1.html 1062108-1-ref.html
 == 1062792-1.html 1062792-1-ref.html
 == 1062963-floatmanager-reflow.html 1062963-floatmanager-reflow-ref.html
-test-pref(dom.webcomponents.shadowdom.enabled,true) == 1066554-1.html 1066554-1-ref.html
+test-pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == 1066554-1.html 1066554-1-ref.html
 == 1069716-1.html 1069716-1-ref.html
 == 1078262-1.html about:blank
 test-pref(layout.testing.overlay-scrollbars.always-visible,false) == 1081072-1.html 1081072-1-ref.html
 fails-if(webrender) == 1081185-1.html 1081185-1-ref.html
 == 1097437-1.html 1097437-1-ref.html
 == 1103258-1.html 1103258-1-ref.html # assertion crash test with layers culling test
 == 1105137-1.html 1105137-1-ref.html
 fuzzy-if(d2d,36,304) fuzzy-if(/^Windows\x20NT\x2010\.0/.test(http.oscpu)&&d2d,139,701) == 1116480-1-fakeitalic-overflow.html 1116480-1-fakeitalic-overflow-ref.html

--- a/layout/reftests/mathml/reftest.list
+++ b/layout/reftests/mathml/reftest.list
@@ -362,17 +362,17 @@ fuzzy-if(OSX,1,100) fuzzy-if(skiaContent
 == mfrac-C-2.html mfrac-C-2-ref.html
 == mfrac-C-3.html mfrac-C-3-ref.html
 == mfrac-C-4.html mfrac-C-4-ref.html
 fuzzy-if(OSX,1,100) fuzzy-if(skiaContent,1,14) == mfrac-D-1.html mfrac-D-1-ref.html
 == mfrac-D-2.html mfrac-D-2-ref.html
 == mfrac-D-3.html mfrac-D-3-ref.html
 == mfrac-D-4.html mfrac-D-4-ref.html
 == mfrac-E-1.html mfrac-E-1-ref.html
-test-pref(dom.webcomponents.shadowdom.enabled,true) == shadow-dom-1.html shadow-dom-1-ref.html
+test-pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == shadow-dom-1.html shadow-dom-1-ref.html
 pref(dom.meta-viewport.enabled,true) pref(font.size.inflation.emPerLine,25) == font-inflation-1.html font-inflation-1-ref.html
 test-pref(font.minimum-size.x-math,40) == default-font.html default-font-ref.html
 != radicalbar-1.html about:blank
 != radicalbar-1a.html about:blank
 != radicalbar-1b.html about:blank
 != radicalbar-1c.html about:blank
 fails-if(webrender) != radicalbar-1d.html about:blank
 != radicalbar-2.html about:blank

--- a/layout/reftests/webcomponents/reftest.list
+++ b/layout/reftests/webcomponents/reftest.list
@@ -1,23 +1,23 @@
-pref(dom.webcomponents.shadowdom.enabled,true) == cross-tree-selection-1.html cross-tree-selection-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-shadow-1.html basic-shadow-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-shadow-2.html basic-shadow-2-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-shadow-3.html basic-shadow-3-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-shadow-4.html basic-shadow-4-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == fallback-content-1.html fallback-content-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == remove-insertion-point-1.html remove-insertion-point-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == nested-insertion-point-1.html nested-insertion-point-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == update-dist-node-descendants-1.html update-dist-node-descendants-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) fuzzy-if(Android,2,7) == input-transition-1.html input-transition-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == dynamic-insertion-point-distribution-1.html dynamic-insertion-point-distribution-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == dynamic-insertion-point-distribution-2.html dynamic-insertion-point-distribution-2-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == remove-append-shadow-host-1.html remove-append-shadow-host-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == reframe-shadow-child-1.html reframe-shadow-child-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == reframe-shadow-child-2.html reframe-shadow-child-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == style-sharing.html style-sharing-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == cross-tree-selection-1.html cross-tree-selection-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-shadow-1.html basic-shadow-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-shadow-2.html basic-shadow-2-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-shadow-3.html basic-shadow-3-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-shadow-4.html basic-shadow-4-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == fallback-content-1.html fallback-content-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == remove-insertion-point-1.html remove-insertion-point-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == nested-insertion-point-1.html nested-insertion-point-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == update-dist-node-descendants-1.html update-dist-node-descendants-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) fuzzy-if(Android,2,7) == input-transition-1.html input-transition-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == dynamic-insertion-point-distribution-1.html dynamic-insertion-point-distribution-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == dynamic-insertion-point-distribution-2.html dynamic-insertion-point-distribution-2-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == remove-append-shadow-host-1.html remove-append-shadow-host-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == reframe-shadow-child-1.html reframe-shadow-child-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == reframe-shadow-child-2.html reframe-shadow-child-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == style-sharing.html style-sharing-ref.html
 pref(dom.webcomponents.shadowdom.enabled,true) skip-if(!stylo||styloVsGecko) == style-sharing-across-shadow.html style-sharing-ref.html # bug 1412400
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-slot-1.html basic-slot-1-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-slot-2.html basic-slot-2-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-slot-3.html basic-slot-3-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-slot-4.html basic-slot-3-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-slot-5.html basic-slot-5-ref.html
-pref(dom.webcomponents.shadowdom.enabled,true) == basic-slot-6.html basic-slot-6-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-slot-1.html basic-slot-1-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-slot-2.html basic-slot-2-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-slot-3.html basic-slot-3-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-slot-4.html basic-slot-3-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-slot-5.html basic-slot-5-ref.html
+pref(dom.webcomponents.shadowdom.enabled,true) fails-if(!stylo||styloVsGecko) == basic-slot-6.html basic-slot-6-ref.html

--- a/testing/web-platform/meta/css/css-scoping/__dir__.ini
+++ b/testing/web-platform/meta/css/css-scoping/__dir__.ini
@@ -1,2 +1,3 @@
 prefs: [dom.webcomponents.shadowdom.enabled:true]
-
+disabled:
+  if not stylo: Shadow DOM is stylo-only

--- a/testing/web-platform/meta/css/selectors/focus-within-shadow-001.html.ini
+++ b/testing/web-platform/meta/css/selectors/focus-within-shadow-001.html.ini
@@ -1,2 +1,5 @@
 [focus-within-shadow-001.html]
+  disabled:
+    if not stylo: Shadow DOM is stylo-only
   expected: FAIL
+  bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1441022

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/meta/css/selectors/focus-within-shadow-002.html.ini
@@ -0,0 +1,3 @@
+[focus-within-shadow-001.html]
+  disabled:
+    if not stylo: Shadow DOM is stylo-only

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/meta/css/selectors/focus-within-shadow-003.html.ini
@@ -0,0 +1,3 @@
+[focus-within-shadow-001.html]
+  disabled:
+    if not stylo: Shadow DOM is stylo-only

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/meta/css/selectors/focus-within-shadow-004.html.ini
@@ -0,0 +1,3 @@
+[focus-within-shadow-001.html]
+  disabled:
+    if not stylo: Shadow DOM is stylo-only

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/meta/css/selectors/focus-within-shadow-005.html.ini
@@ -0,0 +1,3 @@
+[focus-within-shadow-001.html]
+  disabled:
+    if not stylo: Shadow DOM is stylo-only

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/meta/css/selectors/focus-within-shadow-006.html.ini
@@ -0,0 +1,3 @@
+[focus-within-shadow-001.html]
+  disabled:
+    if not stylo: Shadow DOM is stylo-only

--- a/testing/web-platform/meta/shadow-dom/__dir__.ini
+++ b/testing/web-platform/meta/shadow-dom/__dir__.ini
@@ -1,1 +1,3 @@
 prefs: [dom.webcomponents.shadowdom.enabled:true]
+disabled:
+  if not stylo: Shadow DOM is stylo-only