--- a/dom/base/test/file_bug326337_inner.html
+++ b/dom/base/test/file_bug326337_inner.html
@@ -16,25 +16,29 @@ runTest();
 var xhr;
 
 function runTest() {
   xhr = new XMLHttpRequest();
   xhr.open("GET", "file_bug326337.xml", true);
   xhr.onreadystatechange = function() {
     if (xhr.readyState == 4) {
       check(xhr.responseXML.documentElement.getAttribute("root"));
-      SpecialPowers.wrap(parent).location.hash = "#done";
+      SpecialPowers.spawn(parent, [], () => {
+        content.location.hash = "#done";
+      });
     }
   }
   xhr.send(null);
 }
 
 function check(attr) {
   if (attr != "yes") {
-    SpeciaPowers.wrap(parent).location.hash = "#fail";
+    SpecialPowers.spawn(parent, [], () => {
+      content.location.hash = "#fail";
+    });
     throw 1;
   }
 }
 
 </script>
 </pre>
 </body>
 </html>

--- a/dom/base/test/mochitest.ini
+++ b/dom/base/test/mochitest.ini
@@ -305,23 +305,21 @@ skip-if = toolkit == 'android' || headle
 [test_bug282547.html]
 [test_bug298064.html]
 [test_bug300992.html]
 [test_bug311681.xml]
 [test_bug313646.html]
 [test_bug320799.html]
 [test_bug322317.html]
 [test_bug326337.html]
-fail-if = fission
 skip-if = fission && debug # Crashes: @ std::_Function_handler<void (mozilla::Tuple<nsresult, mozilla::dom::PBrowserBridgeParent*>&&), mozilla::dom::WindowGlobalParent::ChangeFrameRemoteness(mozilla::dom::BrowsingContext*, nsTSubstring<char16_t> const&, unsigned long, mozilla::ErrorResult&)::$_2>::_M_invoke(std::_Any_data const&, mozilla::Tuple<nsresult, mozilla::dom::PBrowserBridgeParent*>&&)
 [test_bug330925.xhtml]
 [test_bug331959.html]
-skip-if = fission
 [test_bug333064.html]
-skip-if = fission || toolkit == 'android' || headless # Headless: Bug 1405868
+skip-if = toolkit == 'android' || headless # Headless: Bug 1405868
 [test_bug333198.html]
 [test_bug333673.html]
 [test_bug337631.html]
 [test_bug338541.xhtml]
 [test_bug338583.html]
 skip-if = toolkit == 'android'
 [test_bug338679.html]
 [test_bug339494.html]
@@ -831,19 +829,18 @@ support-files =
 [test_setInterval_from_start.html]
 [test_setInterval_uncatchable_exception.html]
 skip-if = debug == false
 [test_settimeout_extra_arguments.html]
 [test_settimeout_inner.html]
 [test_setTimeoutWith0.html]
 [test_setting_opener.html]
 [test_shared_compartment1.html]
+[test_shared_compartment2.html]
 fail-if = fission
-[test_shared_compartment2.html]
-skip-if = fission # Times out in weird ways.
 [test_structuredclone_backref.html]
 [test_style_cssText.html]
 [test_text_wholeText.html]
 [test_textnode_normalize_in_selection.html]
 [test_textnode_split_in_selection.html]
 [test_timeout_clamp.html]
 skip-if = debug == true && toolkit == 'android' # Timing dependent, skip slow debug android builds
 [test_timer_flood.html]
@@ -877,12 +874,12 @@ fail-if = fission
 [test_window_extensible.html]
 [test_window_indexing.html]
 [test_window_keys.html]
 [test_window_named_frame_enumeration.html]
 [test_window_own_props.html]
 [test_window_proto.html]
 [test_writable-replaceable.html]
 [test_x-frame-options.html]
-fail-if = fission
+fail-if = fission # Cross-origin X-Frame-Options
 skip-if = toolkit == 'android' && debug && !is_fennec
 [test_youtube_flash_embed.html]
 # Please keep alphabetical order.

--- a/dom/base/test/test_bug590812.html
+++ b/dom/base/test/test_bug590812.html
@@ -12,17 +12,25 @@
 <iframe src="http://noxul.example.com/tests/dom/base/test/file_bug590812.xml"></iframe>
 <iframe src="file_bug590812.xml"></iframe>
 <iframe src="file_bug590812-ref.xhtml"></iframe>
 <pre id="test">
 <script class="testbody" type="application/javascript">
 
 SimpleTest.waitForExplicitFinish();
 
-function runTest() {
+async function runTest() {
+  // FIXME(Fission): The load event fires before cross-origin iframes have
+  // loaded (bug 1559841).
+  if (SpecialPowers.useRemoteSubframes) {
+    for (let i = 0; i < 100; i++) {
+      await new Promise(resolve => setTimeout(resolve, 0));
+    }
+  }
+
   sNoXUL = snapshotWindow(window.frames[0], false);
   sWithXUL = snapshotWindow(window.frames[1], false);
   sRef = snapshotWindow(window.frames[2], false);
   let res;
   ok(compareSnapshots(sNoXUL, sRef, true)[0],
      "noxul domain same as ref");
   ok(compareSnapshots(sWithXUL, sRef, true)[0],
      "xul supporting domain same as ref");

--- a/dom/base/test/test_x-frame-options.html
+++ b/dom/base/test/test_x-frame-options.html
@@ -12,102 +12,138 @@
 </div>
 
 <iframe style="width:100%;height:300px;" id="harness"></iframe>
 <script class="testbody" type="text/javascript">
 
 var path = "/tests/dom/base/test/";
 var isUnique = SpecialPowers.getBoolPref("security.data_uri.unique_opaque_origin");
 
-var testFramesLoaded = function() {
-  var harness = SpecialPowers.wrap(document).getElementById("harness");
+var testFramesLoaded = async function() {
+  var harness = document.getElementById("harness").contentDocument;
+
+  // FIXME(Fission): The load event fires before cross-origin iframes have
+  // loaded (bug 1559841).
+  if (SpecialPowers.useRemoteSubframes) {
+    for (let i = 0; i < 100; i++) {
+      await new Promise(resolve => setTimeout(resolve, 0));
+    }
+  }
 
   // iframe from same origin, no X-F-O header - should load
-  var frame = harness.contentDocument.getElementById("control1");
-  var test1 = frame.contentDocument.getElementById("test").textContent;
-  is(test1, "control1", "test control1");
+  var frame = harness.getElementById("control1");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test1 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test1, "control1", "test control1");
+  });
 
   // iframe from different origin, no X-F-O header - should load
-  frame = harness.contentDocument.getElementById("control2");
-  var test2 = frame.contentDocument.getElementById("test").textContent;
-  is(test2, "control2", "test control2");
+  frame = harness.getElementById("control2");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test2 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test2, "control2", "test control2");
+  });
 
   // iframe from same origin, X-F-O: DENY - should not load
-  frame = harness.contentDocument.getElementById("deny");
-  var test3 = frame.contentDocument.getElementById("test");
-  is(test3, null, "test deny");
+  frame = harness.getElementById("deny");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test3 = this.content.document.getElementById("test");
+    Assert.equal(test3, null, "test deny");
+  });
 
   // iframe from same origin, X-F-O: SAMEORIGIN - should load
-  frame = harness.contentDocument.getElementById("sameorigin1");
-  var test4 = frame.contentDocument.getElementById("test").textContent;
-  is(test4, "sameorigin1", "test sameorigin1");
+  frame = harness.getElementById("sameorigin1");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test4 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test4, "sameorigin1", "test sameorigin1");
+  });
 
   // iframe from different origin, X-F-O: SAMEORIGIN - should not load
-  frame = harness.contentDocument.getElementById("sameorigin2");
-  var test5 = frame.contentDocument.getElementById("test");
-  is(test5, null, "test sameorigin2");
+  frame = harness.getElementById("sameorigin2");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test5 = this.content.document.getElementById("test");
+    Assert.equal(test5, null, "test sameorigin2");
+  });
 
   // iframe from different origin, X-F-O: SAMEORIGIN, SAMEORIGIN - should not load
-  frame = harness.contentDocument.getElementById("sameorigin5");
-  var test6 = frame.contentDocument.getElementById("test");
-  is(test6, null, "test sameorigin5");
+  frame = harness.getElementById("sameorigin5");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test6 = this.content.document.getElementById("test");
+    Assert.equal(test6, null, "test sameorigin5");
+  });
 
   // iframe from same origin, X-F-O: SAMEORIGIN, SAMEORIGIN - should load
-  frame = harness.contentDocument.getElementById("sameorigin6");
-  var test7 = frame.contentDocument.getElementById("test").textContent;
-  is(test7, "sameorigin6", "test sameorigin6");
+  frame = harness.getElementById("sameorigin6");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test7 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test7, "sameorigin6", "test sameorigin6");
+  });
 
   // iframe from same origin, X-F-O: SAMEORIGIN,SAMEORIGIN, SAMEORIGIN - should load
-  frame = harness.contentDocument.getElementById("sameorigin7");
-  var test8 = frame.contentDocument.getElementById("test").textContent;
-  is(test8, "sameorigin7", "test sameorigin7");
+  frame = harness.getElementById("sameorigin7");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test8 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test8, "sameorigin7", "test sameorigin7");
+  });
 
   // iframe from same origin, X-F-O: SAMEORIGIN,SAMEORIGIN, SAMEORIGIN - should not load
-  frame = harness.contentDocument.getElementById("sameorigin8");
-  var test9 = frame.contentDocument.getElementById("test");
-  is(test9, null, "test sameorigin8");
+  frame = harness.getElementById("sameorigin8");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test9 = this.content.document.getElementById("test");
+    Assert.equal(test9, null, "test sameorigin8");
+  });
 
   // iframe from same origin, X-F-O: DENY,SAMEORIGIN - should not load
-  frame = harness.contentDocument.getElementById("mixedpolicy");
-  var test10 = frame.contentDocument.getElementById("test");
-  is(test10, null, "test mixedpolicy");
+  frame = harness.getElementById("mixedpolicy");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test10 = this.content.document.getElementById("test");
+    Assert.equal(test10, null, "test mixedpolicy");
+  });
 
   // iframe from different origin, allow-from: this origin - should load
-  frame = harness.contentDocument.getElementById("allow-from-allow");
-  var test11 = frame.contentDocument.getElementById("test").textContent;
-  is(test11, "allow-from-allow", "test allow-from-allow");
+  frame = harness.getElementById("allow-from-allow");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test11 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test11, "allow-from-allow", "test allow-from-allow");
+  });
 
   // iframe from different origin, with allow-from: other - should load as we no longer support allow-from (Bug 1301529)
-  frame = harness.contentDocument.getElementById("allow-from-deny");
-  var test12 = frame.contentDocument.getElementById("test");
-  isnot(test12, null, "test allow-from-deny");
+  frame = harness.getElementById("allow-from-deny");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test12 = this.content.document.getElementById("test");
+    Assert.notEqual(test12, null, "test allow-from-deny");
+  });
 
   // iframe from different origin, X-F-O: SAMEORIGIN, multipart - should not load
-  frame = harness.contentDocument.getElementById("sameorigin-multipart");
-  var test13 = frame.contentDocument.getElementById("test");
-  is(test13, null, "test sameorigin-multipart");
+  frame = harness.getElementById("sameorigin-multipart");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test13 = this.content.document.getElementById("test");
+    Assert.equal(test13, null, "test sameorigin-multipart");
+  });
 
   // iframe from same origin, X-F-O: SAMEORIGIN, multipart - should load
-  frame = harness.contentDocument.getElementById("sameorigin-multipart2");
-  var test14 = frame.contentDocument.getElementById("test").textContent;
-  is(test14, "sameorigin-multipart2", "test sameorigin-multipart2");
+  frame = harness.getElementById("sameorigin-multipart2");
+  await SpecialPowers.spawn(frame, [], () => {
+    var test14 = this.content.document.getElementById("test").textContent;
+    Assert.equal(test14, "sameorigin-multipart2", "test sameorigin-multipart2");
+  });
 
 
   // frames from bug 836132 tests, no longer supported allow-from
   {
-    frame = harness.contentDocument.getElementById("allow-from-allow-1");
+    frame = harness.getElementById("allow-from-allow-1");
     var theTestResult = frame.contentDocument.getElementById("test");
     isnot(theTestResult, null, "test afa1 should have been allowed");
     if(theTestResult) {
       is(theTestResult.textContent, "allow-from-allow-1", "test allow-from-allow-1");
     }
   }
   // Verify allow-from no longer works
   for (var i = 1; i<=14; i++) {
-    frame = harness.contentDocument.getElementById("allow-from-deny-" + i);
+    frame = harness.getElementById("allow-from-deny-" + i);
     var theTestResult = frame.contentDocument.getElementById("test");
     isnot(theTestResult, null, "test allow-from-deny-" + i);
   }
 
   // call tests to check principal comparison, e.g. a document can open a window
   // to a data: or javascript: document which frames an
   // X-Frame-Options: SAMEORIGIN document and the frame should load
   testFrameInJSURI();