--- a/browser/base/content/test/siteIdentity/browser.ini
+++ b/browser/base/content/test/siteIdentity/browser.ini
@@ -114,12 +114,11 @@ support-files =
 [browser_check_identity_state.js]
 [browser_iframe_navigation.js]
 support-files =
   iframe_navigation.html
 [browser_navigation_failures.js]
 [browser_secure_transport_insecure_scheme.js]
 [browser_ignore_same_page_navigation.js]
 [browser_mixed_content_with_navigation.js]
-tags = mcb
 support-files =
   file_mixedPassiveContent.html
   file_bug1045809_1.html

--- a/docshell/base/BrowsingContext.h
+++ b/docshell/base/BrowsingContext.h
@@ -127,20 +127,17 @@ class WindowProxyHolder;
   FIELD(UserAgentOverride, nsString)                                         \
   FIELD(EmbedderElementType, Maybe<nsString>)                                \
   FIELD(MessageManagerGroup, nsString)                                       \
   FIELD(MaxTouchPointsOverride, uint8_t)                                     \
   FIELD(FullZoom, float)                                                     \
   FIELD(WatchedByDevtools, bool)                                             \
   FIELD(TextZoom, float)                                                     \
   /* See nsIRequest for possible flags. */                                   \
-  FIELD(DefaultLoadFlags, uint32_t)                                          \
-  /* Mixed-Content: If the corresponding documentURI is https,               \
-   * then this flag is true. */                                              \
-  FIELD(IsSecure, bool)
+  FIELD(DefaultLoadFlags, uint32_t)
 
 // BrowsingContext, in this context, is the cross process replicated
 // environment in which information about documents is stored. In
 // particular the tree structure of nested browsing contexts is
 // represented by the tree of BrowsingContexts.
 //
 // The tree of BrowsingContexts is created in step with its
 // corresponding nsDocShell, and when nsDocShells are connected

--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -4783,51 +4783,53 @@ nsDocShell::GetFailedChannel(nsIChannel*
 NS_IMETHODIMP
 nsDocShell::GetMixedContentChannel(nsIChannel** aMixedContentChannel) {
   NS_ENSURE_ARG_POINTER(aMixedContentChannel);
   NS_IF_ADDREF(*aMixedContentChannel = mMixedContentChannel);
   return NS_OK;
 }
 
 NS_IMETHODIMP
-nsDocShell::GetAllowMixedContentAndConnectionData(bool* aAllowMixedContent) {
+nsDocShell::GetAllowMixedContentAndConnectionData(
+    bool* aRootHasSecureConnection, bool* aAllowMixedContent,
+    bool* aIsRootDocShell) {
+  *aRootHasSecureConnection = true;
   *aAllowMixedContent = false;
-
-  // If there is a rootDocShell and calling GetMixedContentChannel() on that
-  // rootShell returns a non null mixedContentChannel indicates that the
-  // document has Mixed Active Content that was initially blocked from loading,
-  // but the user has choosen to override the block and allow the content to
-  // load.
-  // mMixedContentChannel is set to the document's channel when the user allows
-  // mixed content. The MixedContentBlocker content policy checks if the
-  // document's root channel matches the mMixedContentChannel.
-
-  nsCOMPtr<nsIDocShell> rootShell = mBrowsingContext->Top()->GetDocShell();
-  // XXX Fission: Cross origin iframes can not access the top-level docshell.
-  // Bug 1632160: Remove GetAllowMixedContentAndConnectionData from
-  // nsIDocShell and expose similar functionality on BrowsingContext
-  if (!rootShell) {
-    return NS_OK;
-  }
-
-  nsCOMPtr<nsIChannel> mixedChannel;
-  rootShell->GetMixedContentChannel(getter_AddRefs(mixedChannel));
-  if (!mixedChannel) {
-    return NS_OK;
-  }
-
-  RefPtr<Document> rootDoc = rootShell->GetDocument();
-  if (!rootDoc) {
-    return NS_OK;
-  }
-
-  // Check the root doc's channel against the root docShell's
-  // mMixedContentChannel to see if they are the same. If they are the same,
-  // the user has overriden the block.
-  *aAllowMixedContent = (mixedChannel == rootDoc->GetChannel());
+  *aIsRootDocShell = false;
+
+  nsCOMPtr<nsIDocShellTreeItem> sameTypeRoot;
+  GetInProcessSameTypeRootTreeItem(getter_AddRefs(sameTypeRoot));
+  NS_ASSERTION(
+      sameTypeRoot,
+      "No document shell root tree item from document shell tree item!");
+  *aIsRootDocShell =
+      sameTypeRoot.get() == static_cast<nsIDocShellTreeItem*>(this);
+
+  // now get the document from sameTypeRoot
+  RefPtr<Document> rootDoc = sameTypeRoot->GetDocument();
+  if (rootDoc) {
+    nsCOMPtr<nsIPrincipal> rootPrincipal = rootDoc->NodePrincipal();
+
+    // For things with system principal (e.g. scratchpad) there is no uri
+    // aRootHasSecureConnection should be false.
+    nsCOMPtr<nsIURI> rootUri = rootPrincipal->GetURI();
+    if (rootPrincipal->IsSystemPrincipal() || !rootUri ||
+        !SchemeIsHTTPS(rootUri)) {
+      *aRootHasSecureConnection = false;
+    }
+
+    // Check the root doc's channel against the root docShell's
+    // mMixedContentChannel to see if they are the same. If they are the same,
+    // the user has overriden the block.
+    nsCOMPtr<nsIDocShell> rootDocShell = do_QueryInterface(sameTypeRoot);
+    nsCOMPtr<nsIChannel> mixedChannel;
+    rootDocShell->GetMixedContentChannel(getter_AddRefs(mixedChannel));
+    *aAllowMixedContent =
+        mixedChannel && (mixedChannel == rootDoc->GetChannel());
+  }
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsDocShell::SetVisibility(bool aVisibility) {
   // Show()/Hide() may change mContentViewer.
   nsCOMPtr<nsIContentViewer> cv = mContentViewer;

--- a/docshell/base/nsIDocShell.idl
+++ b/docshell/base/nsIDocShell.idl
@@ -727,18 +727,21 @@ interface nsIDocShell : nsIDocShellTreeI
    * will be false, mMixedContentChannel will remain null since blocking active content has
    * been disabled and hence mMixedContentChannel will never be set.
    */
   attribute nsIChannel mixedContentChannel;
 
   /**
    * Checks whether the channel associated with the root docShell is equal to
    * mMixedContentChannel. If they are the same, allowMixedContent is set to true.
+   * Checks if the root document has a secure connection. If it is, sets
+   * rootHasSecureConnection to true. If the docShell is the root doc shell,
+   * isRootDocShell is set to true.
    */
-  void GetAllowMixedContentAndConnectionData(out boolean allowMixedContent);
+  void GetAllowMixedContentAndConnectionData(out boolean rootHasSecureConnection, out boolean allowMixedContent, out boolean isRootDocShell);
 
 
   /**
    * Are plugins allowed in the current document loaded in this docshell ?
    * (if there is one). This depends on whether plugins are allowed by this
    * docshell itself or if the document is sandboxed and hence plugins should
    * not be allowed.
    */

--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -3588,24 +3588,16 @@ void Document::SetDocumentURI(nsIURI* aU
     Unused << thirdPartyUtil->GetBaseDomain(mDocumentURI, mBaseDomain);
   }
 
   // Tell our WindowGlobalParent that the document's URI has been changed.
   nsPIDOMWindowInner* inner = GetInnerWindow();
   if (inner && inner->GetWindowGlobalChild()) {
     inner->GetWindowGlobalChild()->SetDocumentURI(mDocumentURI);
   }
-
-  auto* browsingContext = GetBrowsingContext();
-  if (browsingContext) {
-    nsCOMPtr<nsIURI> innerDocURI = NS_GetInnermostURI(mDocumentURI);
-    if (innerDocURI) {
-      browsingContext->SetIsSecure(innerDocURI->SchemeIs("https"));
-    }
-  }
 }
 
 static void GetFormattedTimeString(PRTime aTime,
                                    nsAString& aFormattedTimeString) {
   PRExplodedTime prtime;
   PR_ExplodeTime(aTime, PR_LocalTimeParameters, &prtime);
   // "MM/DD/YYYY hh:mm:ss"
   char formatedTime[24];

--- a/dom/security/nsMixedContentBlocker.cpp
+++ b/dom/security/nsMixedContentBlocker.cpp
@@ -32,17 +32,16 @@
 #include "nsAsyncRedirectVerifyHelper.h"
 #include "mozilla/LoadInfo.h"
 #include "nsISiteSecurityService.h"
 #include "prnetdb.h"
 
 #include "mozilla/BasePrincipal.h"
 #include "mozilla/Logging.h"
 #include "mozilla/StaticPrefs_dom.h"
-#include "mozilla/StaticPrefs_fission.h"
 #include "mozilla/StaticPrefs_security.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/ipc/URIUtils.h"
 #include "mozilla/net/DNS.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -827,71 +826,89 @@ nsresult nsMixedContentBlocker::ShouldLo
         document->InnerWindowID(),
         !!document->NodePrincipal()->OriginAttributesRef().mPrivateBrowsingId);
     *aDecision = REJECT_REQUEST;
     return NS_OK;
   }
 
   // Determine if the rootDoc is https and if the user decided to allow Mixed
   // Content
-  bool rootHasSecureConnection =
-      docShell->GetBrowsingContext()->Top()->GetIsSecure();
+  bool rootHasSecureConnection = false;
   bool allowMixedContent = false;
-  nsresult rv =
-      docShell->GetAllowMixedContentAndConnectionData(&allowMixedContent);
+  bool isRootDocShell = false;
+  nsresult rv = docShell->GetAllowMixedContentAndConnectionData(
+      &rootHasSecureConnection, &allowMixedContent, &isRootDocShell);
   if (NS_FAILED(rv)) {
     *aDecision = REJECT_REQUEST;
     return rv;
   }
 
+  // Get the sameTypeRoot tree item from the docshell
+  nsCOMPtr<nsIDocShellTreeItem> sameTypeRoot;
+  docShell->GetInProcessSameTypeRootTreeItem(getter_AddRefs(sameTypeRoot));
+  NS_ASSERTION(sameTypeRoot, "No root tree item from docshell!");
+
   // When navigating an iframe, the iframe may be https
   // but its parents may not be.  Check the parents to see if any of them are
   // https. If none of the parents are https, allow the load.
   if (aContentType == TYPE_SUBDOCUMENT && !rootHasSecureConnection) {
     bool httpsParentExists = false;
 
-    RefPtr<BrowsingContext> curBC = docShell->GetBrowsingContext();
+    nsCOMPtr<nsIDocShellTreeItem> parentTreeItem;
+    parentTreeItem = docShell;
+
+    while (!httpsParentExists && parentTreeItem) {
+      nsCOMPtr<nsIWebNavigation> parentAsNav(do_QueryInterface(parentTreeItem));
+      NS_ASSERTION(parentAsNav,
+                   "No web navigation object from parent's docshell tree item");
+      nsCOMPtr<nsIURI> parentURI;
+
+      parentAsNav->GetCurrentURI(getter_AddRefs(parentURI));
+      if (!parentURI) {
+        // if getting the URI fails, assume there is a https parent and break.
+        httpsParentExists = true;
+        break;
+      }
 
-    while (!httpsParentExists && curBC) {
-      httpsParentExists = curBC->GetIsSecure();
-      curBC = curBC->GetParent();
-    }
+      nsCOMPtr<nsIURI> innerParentURI = NS_GetInnermostURI(parentURI);
+      if (!innerParentURI) {
+        NS_ERROR("Can't get innerURI from parentURI");
+        *aDecision = REJECT_REQUEST;
+        return NS_OK;
+      }
+
+      httpsParentExists = innerParentURI->SchemeIs("https");
+
+      // When the parent and the root are the same, we have traversed all the
+      // way up the same type docshell tree.  Break out of the while loop.
+      if (sameTypeRoot == parentTreeItem) {
+        break;
+      }
+
+      // update the parent to the grandparent.
+      nsCOMPtr<nsIDocShellTreeItem> newParentTreeItem;
+      parentTreeItem->GetInProcessSameTypeParent(
+          getter_AddRefs(newParentTreeItem));
+      parentTreeItem = newParentTreeItem;
+    }  // end while loop.
 
     if (!httpsParentExists) {
       *aDecision = nsIContentPolicy::ACCEPT;
       return NS_OK;
     }
   }
 
-  // Get the root document from the rootShell
-  nsCOMPtr<nsIDocShell> rootShell =
-      docShell->GetBrowsingContext()->Top()->GetDocShell();
-  nsCOMPtr<Document> rootDoc = rootShell ? rootShell->GetDocument() : nullptr;
-
-  // TODO Fission: Bug 1631405: Make Mixed Content UI fission compatible
-  // At this point we know it's a mixed content load, which means we we would
-  // allow mixed passive content to load but only allow mixed active content
-  // if the user has updated prefs or overriden mixed content using the UI.
-  // In fission however, we might not have access to the rootShell or RootDoc
-  // so might not be able to access Mixed Content UI. Until we have fixed
-  // Bug 1631405 we assume default behavior and allow mixed passive content
-  // but block mixed active content in fission.
-  if (StaticPrefs::fission_autostart()) {
-    if (!rootShell || !rootDoc) {
-      if (classification == eMixedDisplay) {
-        *aDecision = nsIContentPolicy::ACCEPT;
-        return NS_OK;
-      }
-      *aDecision = nsIContentPolicy::REJECT_REQUEST;
-      return NS_OK;
-    }
-  }
+  // Get the root document from the sameTypeRoot
+  nsCOMPtr<Document> rootDoc = sameTypeRoot->GetDocument();
+  NS_ASSERTION(rootDoc, "No root document from document shell root tree item.");
 
   nsDocShell* nativeDocShell = nsDocShell::Cast(docShell);
-
+  nsCOMPtr<nsIDocShell> rootShell = do_GetInterface(sameTypeRoot);
+  NS_ASSERTION(rootShell,
+               "No root docshell from document shell root tree item.");
   uint32_t state = nsIWebProgressListener::STATE_IS_BROKEN;
   nsCOMPtr<nsISecureBrowserUI> securityUI;
   rootShell->GetSecurityUI(getter_AddRefs(securityUI));
   // If there is no securityUI, document doesn't have a security state.
   // Allow load and return early.
   if (!securityUI) {
     *aDecision = nsIContentPolicy::ACCEPT;
     return NS_OK;

--- a/security/manager/ssl/tests/mochitest/mixedcontent/mochitest.ini
+++ b/security/manager/ssl/tests/mochitest/mixedcontent/mochitest.ini
@@ -59,11 +59,12 @@ disabled=intermitently fails, quite ofte
 [test_unsecureIframe.html]
 [test_unsecureIframe2.html]
 [test_unsecureIframeMetaRedirect.html]
 disabled=intermittently fails, less often, bug 487632
 [test_unsecureIframeRedirect.html]
 fail-if = fission
 [test_unsecurePicture.html]
 [test_unsecurePictureDup.html]
+skip-if = fission && debug
 [test_unsecurePictureInIframe.html]
 [test_unsecureRedirect.html]
 skip-if = verify && debug && (os == 'linux' || os == 'mac')