--- a/dom/webidl/ChannelWrapper.webidl
+++ b/dom/webidl/ChannelWrapper.webidl
@@ -127,28 +127,16 @@ interface ChannelWrapper {
   readonly attribute long long windowId;
 
   [Cached, Constant]
   readonly attribute long long parentWindowId;
 
   [Cached, Pure]
   readonly attribute nsISupports? browserElement;
 
-  /**
-   * Returns an array of objects that combine the url and frameId from the
-   * ancestorPrincipals and ancestorOuterWindowIDs on loadInfo.
-   * The immediate parent is the first entry, the last entry is always the top
-   * level frame.  It will be an empty list for toplevel window loads and
-   * non-subdocument resource loads within a toplevel window.  For the latter,
-   * originURL will provide information on what window is doing the load.  It
-   * will be null if the request is not associated with a window (e.g. XHR with
-   * mozBackgroundRequest = true).
-   */
-  [Cached, Frozen, GetterThrows, Pure]
-  readonly attribute sequence<MozFrameAncestorInfo>? frameAncestors;
 
   [Throws]
   object getRequestHeaders();
 
   [Throws]
   object getResponseHeaders();
 
   [Throws]
@@ -164,22 +152,8 @@ dictionary MozProxyInfo {
   required ByteString type;
 
   required boolean proxyDNS;
 
   ByteString? username = null;
 
   unsigned long failoverTimeout;
 };
-
-/**
- * MozFrameAncestorInfo combines loadInfo::AncestorPrincipals with
- * loadInfo::AncestorOuterWindowIDs for easier access in the WebRequest API.
- *
- * url represents the parent of the loading window.
- * frameId is the outerWindowID for the parent of the loading window.
- *
- * For further details see nsILoadInfo.idl and nsIDocument::AncestorPrincipals.
- */
-dictionary MozFrameAncestorInfo {
-  required ByteString url;
-  required unsigned long long frameId;
-};

--- a/ipc/glue/BackgroundUtils.cpp
+++ b/ipc/glue/BackgroundUtils.cpp
@@ -365,23 +365,16 @@ LoadInfoToLoadInfoArgs(nsILoadInfo *aLoa
   nsTArray<RedirectHistoryEntryInfo> redirectChain;
   for (const nsCOMPtr<nsIRedirectHistoryEntry>& redirectEntry :
        aLoadInfo->RedirectChain()) {
     RedirectHistoryEntryInfo* entry = redirectChain.AppendElement();
     rv = RHEntryToRHEntryInfo(redirectEntry, entry);
     NS_ENSURE_SUCCESS(rv, rv);
   }
 
-  nsTArray<PrincipalInfo> ancestorPrincipals;
-  ancestorPrincipals.SetCapacity(aLoadInfo->AncestorPrincipals().Length());
-  for (const auto& principal : aLoadInfo->AncestorPrincipals()) {
-    rv = PrincipalToPrincipalInfo(principal, ancestorPrincipals.AppendElement());
-    NS_ENSURE_SUCCESS(rv, rv);
-  }
-
   *aOptionalLoadInfoArgs =
     LoadInfoArgs(
       loadingPrincipalInfo,
       triggeringPrincipalInfo,
       principalToInheritInfo,
       sandboxedLoadingPrincipalInfo,
       optionalResultPrincipalURI,
       aLoadInfo->GetSecurityFlags(),
@@ -397,18 +390,16 @@ LoadInfoToLoadInfoArgs(nsILoadInfo *aLoa
       aLoadInfo->GetTopOuterWindowID(),
       aLoadInfo->GetFrameOuterWindowID(),
       aLoadInfo->GetEnforceSecurity(),
       aLoadInfo->GetInitialSecurityCheckDone(),
       aLoadInfo->GetIsInThirdPartyContext(),
       aLoadInfo->GetOriginAttributes(),
       redirectChainIncludingInternalRedirects,
       redirectChain,
-      ancestorPrincipals,
-      aLoadInfo->AncestorOuterWindowIDs(),
       aLoadInfo->CorsUnsafeHeaders(),
       aLoadInfo->GetForcePreflight(),
       aLoadInfo->GetIsPreflight(),
       aLoadInfo->GetForceHSTSPriming(),
       aLoadInfo->GetMixedContentWouldBlock(),
       aLoadInfo->GetIsHSTSPriming(),
       aLoadInfo->GetIsHSTSPrimingUpgrade()
       );
@@ -471,25 +462,16 @@ LoadInfoArgsToLoadInfo(const OptionalLoa
   RedirectHistoryArray redirectChain;
   for (const RedirectHistoryEntryInfo& entryInfo : loadInfoArgs.redirectChain()) {
     nsCOMPtr<nsIRedirectHistoryEntry> redirectHistoryEntry =
       RHEntryInfoToRHEntry(entryInfo);
     NS_ENSURE_SUCCESS(rv, rv);
     redirectChain.AppendElement(redirectHistoryEntry.forget());
   }
 
-  nsTArray<nsCOMPtr<nsIPrincipal>> ancestorPrincipals;
-  ancestorPrincipals.SetCapacity(loadInfoArgs.ancestorPrincipals().Length());
-  for (const PrincipalInfo& principalInfo : loadInfoArgs.ancestorPrincipals()) {
-    nsCOMPtr<nsIPrincipal> ancestorPrincipal =
-      PrincipalInfoToPrincipal(principalInfo, &rv);
-    NS_ENSURE_SUCCESS(rv, rv);
-    ancestorPrincipals.AppendElement(ancestorPrincipal.forget());
-  }
-
   nsCOMPtr<nsILoadInfo> loadInfo =
     new mozilla::LoadInfo(loadingPrincipal,
                           triggeringPrincipal,
                           principalToInherit,
                           sandboxedLoadingPrincipal,
                           resultPrincipalURI,
                           loadInfoArgs.securityFlags(),
                           loadInfoArgs.contentPolicyType(),
@@ -504,18 +486,16 @@ LoadInfoArgsToLoadInfo(const OptionalLoa
                           loadInfoArgs.topOuterWindowID(),
                           loadInfoArgs.frameOuterWindowID(),
                           loadInfoArgs.enforceSecurity(),
                           loadInfoArgs.initialSecurityCheckDone(),
                           loadInfoArgs.isInThirdPartyContext(),
                           loadInfoArgs.originAttributes(),
                           redirectChainIncludingInternalRedirects,
                           redirectChain,
-                          Move(ancestorPrincipals),
-                          loadInfoArgs.ancestorOuterWindowIDs(),
                           loadInfoArgs.corsUnsafeHeaders(),
                           loadInfoArgs.forcePreflight(),
                           loadInfoArgs.isPreflight(),
                           loadInfoArgs.forceHSTSPriming(),
                           loadInfoArgs.mixedContentWouldBlock(),
                           loadInfoArgs.isHSTSPriming(),
                           loadInfoArgs.isHSTSPrimingUpgrade()
                           );

--- a/netwerk/base/LoadInfo.cpp
+++ b/netwerk/base/LoadInfo.cpp
@@ -25,21 +25,20 @@
 #include "nsRedirectHistoryEntry.h"
 
 using namespace mozilla::dom;
 
 namespace mozilla {
 namespace net {
 
 static uint64_t
-GatherAncestorOuterWindowIDs(nsPIDOMWindowOuter* aOuter, nsTArray<uint64_t>& aOuterWindowIDs)
+FindTopOuterWindowID(nsPIDOMWindowOuter* aOuter)
 {
   nsCOMPtr<nsPIDOMWindowOuter> outer = aOuter;
   while (nsCOMPtr<nsPIDOMWindowOuter> parent = outer->GetScriptableParentOrNull()) {
-    aOuterWindowIDs.AppendElement(parent->WindowID());
     outer = parent;
   }
   return outer->WindowID();
 }
 
 LoadInfo::LoadInfo(nsIPrincipal* aLoadingPrincipal,
                    nsIPrincipal* aTriggeringPrincipal,
                    nsINode* aLoadingContext,
@@ -110,21 +109,20 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
 
   if (aLoadingContext) {
     nsCOMPtr<nsPIDOMWindowOuter> contextOuter = aLoadingContext->OwnerDoc()->GetWindow();
     if (contextOuter) {
       ComputeIsThirdPartyContext(contextOuter);
       mOuterWindowID = contextOuter->WindowID();
       nsCOMPtr<nsPIDOMWindowOuter> parent = contextOuter->GetScriptableParent();
       mParentOuterWindowID = parent ? parent->WindowID() : mOuterWindowID;
-      mTopOuterWindowID = GatherAncestorOuterWindowIDs(contextOuter, mAncestorOuterWindowIDs);
+      mTopOuterWindowID = FindTopOuterWindowID(contextOuter);
     }
 
     mInnerWindowID = aLoadingContext->OwnerDoc()->InnerWindowID();
-    mAncestorPrincipals = aLoadingContext->OwnerDoc()->AncestorPrincipals();
 
     // When the element being loaded is a frame, we choose the frame's window
     // for the window ID and the frame element's window as the parent
     // window. This is the behavior that Chrome exposes to add-ons.
     // NB: If the frameLoaderOwner doesn't have a frame loader, then the load
     // must be coming from an object (such as a plugin) that's loaded into it
     // instead of a document being loaded. In that case, treat this object like
     // any other non-document-loading element.
@@ -268,23 +266,22 @@ LoadInfo::LoadInfo(nsPIDOMWindowOuter* a
 
   // NB: Ignore the current inner window since we're navigating away from it.
   mOuterWindowID = aOuterWindow->WindowID();
 
   // TODO We can have a parent without a frame element in some cases dealing
   // with the hidden window.
   nsCOMPtr<nsPIDOMWindowOuter> parent = aOuterWindow->GetScriptableParent();
   mParentOuterWindowID = parent ? parent->WindowID() : 0;
-  mTopOuterWindowID = GatherAncestorOuterWindowIDs(aOuterWindow, mAncestorOuterWindowIDs);
+  mTopOuterWindowID = FindTopOuterWindowID(aOuterWindow);
 
   // get the docshell from the outerwindow, and then get the originattributes
   nsCOMPtr<nsIDocShell> docShell = aOuterWindow->GetDocShell();
   MOZ_ASSERT(docShell);
   mOriginAttributes = nsDocShell::Cast(docShell)->GetOriginAttributes();
-  mAncestorPrincipals = nsDocShell::Cast(docShell)->AncestorPrincipals();
 
 #ifdef DEBUG
   if (docShell->ItemType() == nsIDocShellTreeItem::typeChrome) {
     MOZ_ASSERT(mOriginAttributes.mPrivateBrowsingId == 0,
                "chrome docshell shouldn't have mPrivateBrowsingId set.");
   }
 #endif
 }
@@ -311,18 +308,16 @@ LoadInfo::LoadInfo(const LoadInfo& rhs)
   , mFrameOuterWindowID(rhs.mFrameOuterWindowID)
   , mEnforceSecurity(rhs.mEnforceSecurity)
   , mInitialSecurityCheckDone(rhs.mInitialSecurityCheckDone)
   , mIsThirdPartyContext(rhs.mIsThirdPartyContext)
   , mOriginAttributes(rhs.mOriginAttributes)
   , mRedirectChainIncludingInternalRedirects(
       rhs.mRedirectChainIncludingInternalRedirects)
   , mRedirectChain(rhs.mRedirectChain)
-  , mAncestorPrincipals(rhs.mAncestorPrincipals)
-  , mAncestorOuterWindowIDs(rhs.mAncestorOuterWindowIDs)
   , mCorsUnsafeHeaders(rhs.mCorsUnsafeHeaders)
   , mForcePreflight(rhs.mForcePreflight)
   , mIsPreflight(rhs.mIsPreflight)
   , mForceHSTSPriming(rhs.mForceHSTSPriming)
   , mMixedContentWouldBlock(rhs.mMixedContentWouldBlock)
   , mIsHSTSPriming(rhs.mIsHSTSPriming)
   , mIsHSTSPrimingUpgrade(rhs.mIsHSTSPrimingUpgrade)
 {
@@ -346,18 +341,16 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
                    uint64_t aTopOuterWindowID,
                    uint64_t aFrameOuterWindowID,
                    bool aEnforceSecurity,
                    bool aInitialSecurityCheckDone,
                    bool aIsThirdPartyContext,
                    const OriginAttributes& aOriginAttributes,
                    RedirectHistoryArray& aRedirectChainIncludingInternalRedirects,
                    RedirectHistoryArray& aRedirectChain,
-                   nsTArray<nsCOMPtr<nsIPrincipal>>&& aAncestorPrincipals,
-                   const nsTArray<uint64_t>& aAncestorOuterWindowIDs,
                    const nsTArray<nsCString>& aCorsUnsafeHeaders,
                    bool aForcePreflight,
                    bool aIsPreflight,
                    bool aForceHSTSPriming,
                    bool aMixedContentWouldBlock,
                    bool aIsHSTSPriming,
                    bool aIsHSTSPrimingUpgrade)
   : mLoadingPrincipal(aLoadingPrincipal)
@@ -375,18 +368,16 @@ LoadInfo::LoadInfo(nsIPrincipal* aLoadin
   , mOuterWindowID(aOuterWindowID)
   , mParentOuterWindowID(aParentOuterWindowID)
   , mTopOuterWindowID(aTopOuterWindowID)
   , mFrameOuterWindowID(aFrameOuterWindowID)
   , mEnforceSecurity(aEnforceSecurity)
   , mInitialSecurityCheckDone(aInitialSecurityCheckDone)
   , mIsThirdPartyContext(aIsThirdPartyContext)
   , mOriginAttributes(aOriginAttributes)
-  , mAncestorPrincipals(Move(aAncestorPrincipals))
-  , mAncestorOuterWindowIDs(aAncestorOuterWindowIDs)
   , mCorsUnsafeHeaders(aCorsUnsafeHeaders)
   , mForcePreflight(aForcePreflight)
   , mIsPreflight(aIsPreflight)
   , mForceHSTSPriming (aForceHSTSPriming)
   , mMixedContentWouldBlock(aMixedContentWouldBlock)
   , mIsHSTSPriming(aIsHSTSPriming)
   , mIsHSTSPrimingUpgrade(aIsHSTSPrimingUpgrade)
 {
@@ -918,28 +909,16 @@ LoadInfo::GetRedirectChain(JSContext* aC
 }
 
 const RedirectHistoryArray&
 LoadInfo::RedirectChain()
 {
   return mRedirectChain;
 }
 
-const nsTArray<nsCOMPtr<nsIPrincipal>>&
-LoadInfo::AncestorPrincipals()
-{
-  return mAncestorPrincipals;
-}
-
-const nsTArray<uint64_t>&
-LoadInfo::AncestorOuterWindowIDs()
-{
-  return mAncestorOuterWindowIDs;
-}
-
 void
 LoadInfo::SetCorsPreflightInfo(const nsTArray<nsCString>& aHeaders,
                                bool aForcePreflight)
 {
   MOZ_ASSERT(GetSecurityMode() == nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS);
   MOZ_ASSERT(!mInitialSecurityCheckDone);
   mCorsUnsafeHeaders = aHeaders;
   mForcePreflight = aForcePreflight;

--- a/netwerk/base/LoadInfo.h
+++ b/netwerk/base/LoadInfo.h
@@ -110,18 +110,16 @@ private:
            uint64_t aTopOuterWindowID,
            uint64_t aFrameOuterWindowID,
            bool aEnforceSecurity,
            bool aInitialSecurityCheckDone,
            bool aIsThirdPartyRequest,
            const OriginAttributes& aOriginAttributes,
            RedirectHistoryArray& aRedirectChainIncludingInternalRedirects,
            RedirectHistoryArray& aRedirectChain,
-           nsTArray<nsCOMPtr<nsIPrincipal>>&& aAncestorPrincipals,
-           const nsTArray<uint64_t>& aAncestorOuterWindowIDs,
            const nsTArray<nsCString>& aUnsafeHeaders,
            bool aForcePreflight,
            bool aIsPreflight,
            bool aForceHSTSPriming,
            bool aMixedContentWouldBlock,
            bool aIsHSTSPriming,
            bool aIsHSTSPrimingUpgrade);
   LoadInfo(const LoadInfo& rhs);
@@ -165,18 +163,16 @@ private:
   uint64_t                         mTopOuterWindowID;
   uint64_t                         mFrameOuterWindowID;
   bool                             mEnforceSecurity;
   bool                             mInitialSecurityCheckDone;
   bool                             mIsThirdPartyContext;
   OriginAttributes                 mOriginAttributes;
   RedirectHistoryArray             mRedirectChainIncludingInternalRedirects;
   RedirectHistoryArray             mRedirectChain;
-  nsTArray<nsCOMPtr<nsIPrincipal>> mAncestorPrincipals;
-  nsTArray<uint64_t>               mAncestorOuterWindowIDs;
   nsTArray<nsCString>              mCorsUnsafeHeaders;
   bool                             mForcePreflight;
   bool                             mIsPreflight;
 
   bool                             mForceHSTSPriming : 1;
   bool                             mMixedContentWouldBlock : 1;
   bool                             mIsHSTSPriming: 1;
   bool                             mIsHSTSPrimingUpgrade: 1;

--- a/netwerk/base/nsILoadInfo.idl
+++ b/netwerk/base/nsILoadInfo.idl
@@ -18,18 +18,16 @@ interface nsIURI;
 #include "mozilla/LoadTainting.h"
 #include "nsStringFwd.h"
 %}
 
 [ref] native nsIRedirectHistoryEntryArray(const nsTArray<nsCOMPtr<nsIRedirectHistoryEntry>>);
 native OriginAttributes(mozilla::OriginAttributes);
 [ref] native const_OriginAttributesRef(const mozilla::OriginAttributes);
 [ref] native StringArrayRef(const nsTArray<nsCString>);
-[ref] native Uint64ArrayRef(const nsTArray<uint64_t>);
-[ref] native PrincipalArrayRef(const nsTArray<nsCOMPtr<nsIPrincipal>>);
 
 typedef unsigned long nsSecurityFlags;
 
 /**
  * The LoadInfo object contains information about a network load, why it
  * was started, and how we plan on using the resulting response.
  * If a network request is redirected, the new channel will receive a new
  * LoadInfo object. The new object will contain mostly the same
@@ -640,46 +638,16 @@ interface nsILoadInfo : nsISupports
    * A C++-friendly version of redirectChain.
    * Please note that this array has the same lifetime as the
    * loadInfo object - use with caution!
    */
   [noscript, notxpcom, nostdcall, binaryname(RedirectChain)]
   nsIRedirectHistoryEntryArray binaryRedirectChain();
 
   /**
-   * An array of nsIPrincipals which stores the principals of the parent frames,
-   * not including the frame loading this request.  The closest ancestor is at
-   * index zero and the top level ancestor is at the last index.
-   *
-   * The ancestorPrincipals[0] entry for an iframe load will be the principal of
-   * the iframe element's owner document.
-   * The ancestorPrincipals[0] entry for an image loaded in an iframe will be the
-   * principal of the iframe element's owner document.
-   *
-   * See nsIDocument::AncestorPrincipals for more information.
-   *
-   * Please note that this array has the same lifetime as the
-   * loadInfo object - use with caution!
-   */
-  [noscript, notxpcom, nostdcall]
-  PrincipalArrayRef AncestorPrincipals();
-
-
-  /**
-   * An array of outerWindowIDs which correspond to nsILoadInfo::AncestorPrincipals
-   * above.  AncestorOuterWindowIDs[0] is the outerWindowID of the frame
-   * associated with the principal at ancestorPrincipals[0], and so forth.
-   *
-   * Please note that this array has the same lifetime as the
-   * loadInfo object - use with caution!
-   */
-  [noscript, notxpcom, nostdcall]
-  Uint64ArrayRef AncestorOuterWindowIDs();
-
-  /**
    * Sets the list of unsafe headers according to CORS spec, as well as
    * potentially forces a preflight.
    * Note that you do not need to set the Content-Type header. That will be
    * automatically detected as needed.
    *
    * Only call this function when using the SEC_REQUIRE_CORS_DATA_INHERITS mode.
    */
   [noscript, notxpcom, nostdcall]

--- a/netwerk/ipc/NeckoChannelParams.ipdlh
+++ b/netwerk/ipc/NeckoChannelParams.ipdlh
@@ -54,24 +54,16 @@ struct LoadInfoArgs
   uint64_t                    topOuterWindowID;
   uint64_t                    frameOuterWindowID;
   bool                        enforceSecurity;
   bool                        initialSecurityCheckDone;
   bool                        isInThirdPartyContext;
   OriginAttributes            originAttributes;
   RedirectHistoryEntryInfo[]  redirectChainIncludingInternalRedirects;
   RedirectHistoryEntryInfo[]  redirectChain;
-
-  /**
-   * Ancestor data for use with the WebRequest API.
-   * See nsILoadInfo.idl for details.
-   */
-  PrincipalInfo[]             ancestorPrincipals;
-  uint64_t[]                  ancestorOuterWindowIDs;
-
   nsCString[]                 corsUnsafeHeaders;
   bool                        forcePreflight;
   bool                        isPreflight;
   bool                        forceHSTSPriming;
   bool                        mixedContentWouldBlock;
   bool                        isHSTSPriming;
   bool                        isHSTSPrimingUpgrade;
 };

--- a/toolkit/components/extensions/test/mochitest/file_simple_sandboxed_frame.html
+++ b/toolkit/components/extensions/test/mochitest/file_simple_sandboxed_frame.html
@@ -7,17 +7,12 @@
 <body>
 
 <script>
 "use strict";
 
 let req = new XMLHttpRequest();
 req.open("GET", "/xhr_sandboxed");
 req.send();
-
-let sandbox = document.createElement("iframe");
-sandbox.setAttribute("sandbox", "allow-scripts");
-sandbox.setAttribute("src", "file_simple_sandboxed_subframe.html");
-document.documentElement.appendChild(sandbox);
 </script>
 <img src="file_image_great.png"/>
 </body>
 </html>

deleted file mode 100644
--- a/toolkit/components/extensions/test/mochitest/file_simple_sandboxed_subframe.html
+++ /dev/null
@@ -1,10 +0,0 @@
-<!DOCTYPE HTML>
-
-<html>
-<head>
-<meta charset="utf-8">
-</head>
-<body>
-
-</body>
-</html>

--- a/toolkit/components/extensions/test/mochitest/file_simple_xhr_frame2.html
+++ b/toolkit/components/extensions/test/mochitest/file_simple_xhr_frame2.html
@@ -13,12 +13,11 @@ let req = new XMLHttpRequest();
 req.open("GET", "/xhr_resource_2");
 req.send();
 
 let sandbox = document.createElement("iframe");
 sandbox.setAttribute("sandbox", "allow-scripts");
 sandbox.setAttribute("src", "file_simple_sandboxed_frame.html");
 document.documentElement.appendChild(sandbox);
 </script>
-<img src="file_image_redirect.png"/>
-<iframe src="data:text/plain,webRequestTest"/>
+<img src="file_image_bad.png#2"/>
 </body>
 </html>

--- a/toolkit/components/extensions/test/mochitest/mochitest-common.ini
+++ b/toolkit/components/extensions/test/mochitest/mochitest-common.ini
@@ -35,17 +35,16 @@ support-files =
   file_style_redirect.css
   file_script_good.js
   file_script_bad.js
   file_script_redirect.js
   file_script_xhr.js
   file_remote_frame.html
   file_sample.html
   file_simple_sandboxed_frame.html
-  file_simple_sandboxed_subframe.html
   file_simple_xhr.html
   file_simple_xhr_frame.html
   file_simple_xhr_frame2.html
   redirect_auto.sjs
   redirection.sjs
   file_privilege_escalation.html
   file_ext_test_api_injection.js
   file_permission_xhr.html

--- a/toolkit/components/extensions/test/mochitest/test_ext_webrequest_frameId.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_webrequest_frameId.html
@@ -40,129 +40,68 @@ let extensionData = {
 let expected = {
   "file_simple_xhr.html": {
     type: "main_frame",
     toplevel: true,
   },
   "file_image_good.png": {
     type: "image",
     toplevel: true,
-    origin: "file_simple_xhr.html",
   },
   "example.txt": {
     type: "xmlhttprequest",
     toplevel: true,
-    origin: "file_simple_xhr.html",
   },
-  // sub frames will have the origin and first ancestor is the
-  // parent document
   "file_simple_xhr_frame.html": {
     type: "sub_frame",
     toplevelParent: true,
-    origin: "file_simple_xhr.html",
-    parent: "file_simple_xhr.html",
-  },
-  // a resource in a sub frame will have origin of the subframe,
-  // but the ancestor chain starts with the parent document
-  "xhr_resource": {
-    type: "xmlhttprequest",
-    origin: "file_simple_xhr_frame.html",
-    parent: "file_simple_xhr.html",
   },
   "file_image_bad.png": {
     type: "image",
-    depth: 2,
-    origin: "file_simple_xhr_frame.html",
-    parent: "file_simple_xhr.html",
+  },
+  "xhr_resource": {
+    type: "xmlhttprequest",
   },
   "file_simple_xhr_frame2.html": {
     type: "sub_frame",
-    depth: 2,
-    origin: "file_simple_xhr_frame.html",
-    parent: "file_simple_xhr_frame.html",
   },
-  "file_image_redirect.png": {
+  "file_image_bad.png#2": {
     type: "image",
-    depth: 2,
-    origin: "file_simple_xhr_frame2.html",
-    parent: "file_simple_xhr_frame.html",
   },
   "xhr_resource_2": {
     type: "xmlhttprequest",
-    depth: 2,
-    origin: "file_simple_xhr_frame2.html",
-    parent: "file_simple_xhr_frame.html",
   },
-  // Last frame tests content policy frame ancestors.
-  "webRequestTest": {
-    type: "sub_frame",
-    depth: 3,
-    origin: "file_simple_xhr_frame2.html",
-    parent: "file_simple_xhr_frame2.html",
-  },
-  // This is loaded in a sandbox iframe.  originUrl is not availabe for that,
-  // and requests within a sandboxed iframe will additionally have an empty
-  // url on their immediate parent/ancestor.
+  // This is loaded in a sandbox iframe.
   "file_simple_sandboxed_frame.html": {
     type: "sub_frame",
-    depth: 3,
-    parent: "file_simple_xhr_frame2.html",
   },
   "xhr_sandboxed": {
     type: "xmlhttprequest",
     sandboxed: true,
-    depth: 3,
-    parent: "",
   },
   "file_image_great.png": {
     type: "image",
     sandboxed: true,
-    depth: 3,
-    parent: "",
-  },
-  "file_simple_sandboxed_subframe.html": {
-    type: "sub_frame",
-    depth: 4,
-    parent: "",
   },
 };
 
 function checkDetails(details) {
   let url = new URL(details.url);
-  let filename = url.pathname.split(url.protocol == "data:" ? "," : "/").pop();
+  let filename = url.pathname.split("/").pop();
   let expect = expected[filename];
   is(expect.type, details.type, `${details.type} type matches`);
-  if (details.parentFrameId == -1) {
-    is(details.frameAncestors.length, 0, "no ancestors for main_frame requests");
-  } else if (details.parentFrameId == 0) {
-    is(details.frameAncestors.length, 1, "one ancestors for sub_frame requests");
-  } else {
-    ok(details.frameAncestors.length > 1, "have multiple ancestors for deep subframe requests");
-    is(details.frameAncestors.length, expect.depth, "have multiple ancestors for deep subframe requests");
-  }
-  if (details.parentFrameId > -1) {
-    ok(!expect.origin || details.originUrl.includes(expect.origin), "origin url is correct");
-    is(details.frameAncestors[0].frameId, details.parentFrameId, "first ancestor matches request.parentFrameId");
-    ok(details.frameAncestors[0].url.includes(expect.parent), "ancestor parent page correct");
-    is(details.frameAncestors[details.frameAncestors.length - 1].frameId, 0, "last ancestor is always zero");
-    // All our tests should be somewhere within the frame that we set topframe in the query string.  That
-    // frame will always be the last ancestor.
-    ok(details.frameAncestors[details.frameAncestors.length - 1].url.includes("topframe=true"), "last ancestor is always topframe");
-  }
   if (expect.toplevel) {
     is(details.frameId, 0, "expect load at top level");
     is(details.parentFrameId, -1, "expect top level frame to have no parent");
   } else if (details.type == "sub_frame") {
     ok(details.frameId > 0, "expect sub_frame to load into a new frame");
     if (expect.toplevelParent) {
       is(details.parentFrameId, 0, "expect sub_frame to have top level parent");
-      is(details.frameAncestors.length, 1, "one ancestor for top sub_frame request");
     } else {
       ok(details.parentFrameId > 0, "expect sub_frame to have parent");
-      ok(details.frameAncestors.length > 1, "sub_frame has ancestors");
     }
     expect.subframeId = details.frameId;
     expect.parentId = details.parentFrameId;
   } else if (expect.sandboxed) {
     is(details.documentUrl, undefined, "null principal documentUrl for sandboxed request");
   } else {
     // get the parent frame.
     let purl = new URL(details.documentUrl);
@@ -177,27 +116,28 @@ add_task(async function test_webRequest_
   // Clear the image cache, since it gets in the way otherwise.
   let imgTools = SpecialPowers.Cc["@mozilla.org/image/tools;1"].getService(SpecialPowers.Ci.imgITools);
   let cache = imgTools.getImgCacheForDocument(document);
   cache.clearCache(false);
 
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   await extension.startup();
 
-  let a = addLink(`file_simple_xhr.html?topframe=true&nocache=${Math.random()}`);
+  let a = addLink(`file_simple_xhr.html?nocache=${Math.random()}`);
   a.click();
 
   for (let i = 0; i < Object.keys(expected).length; i++) {
     checkDetails(await extension.awaitMessage("onBeforeRequest"));
   }
 
   let closed = extension.awaitMessage("tab-closed");
   extension.sendMessage("close-tab");
   await closed;
   await extension.unload();
 });
+
 </script>
 </head>
 <body>
 <div id="test">Sample text</div>
 
 </body>
 </html>

--- a/toolkit/components/extensions/webrequest/ChannelWrapper.cpp
+++ b/toolkit/components/extensions/webrequest/ChannelWrapper.cpp
@@ -471,70 +471,16 @@ ChannelWrapper::ParentWindowId() const
     } else {
       parentID = loadInfo->GetParentOuterWindowID();
     }
     return NormalizeWindowID(loadInfo, parentID);
   }
   return -1;
 }
 
-void
-ChannelWrapper::GetFrameAncestors(dom::Nullable<nsTArray<dom::MozFrameAncestorInfo>>& aFrameAncestors, ErrorResult& aRv) const
-{
-  nsCOMPtr<nsILoadInfo> loadInfo = GetLoadInfo();
-  if (!loadInfo || WindowId(loadInfo) == 0) {
-    aFrameAncestors.SetNull();
-    return;
-  }
-
-  nsresult rv = GetFrameAncestors(loadInfo, aFrameAncestors.SetValue());
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-  }
-}
-
-nsresult
-ChannelWrapper::GetFrameAncestors(nsILoadInfo* aLoadInfo, nsTArray<dom::MozFrameAncestorInfo>& aFrameAncestors) const
-{
-  const nsTArray<nsCOMPtr<nsIPrincipal>>& ancestorPrincipals = aLoadInfo->AncestorPrincipals();
-  const nsTArray<uint64_t>& ancestorOuterWindowIDs = aLoadInfo->AncestorOuterWindowIDs();
-  uint32_t size = ancestorPrincipals.Length();
-  MOZ_DIAGNOSTIC_ASSERT(size == ancestorOuterWindowIDs.Length());
-  if (size != ancestorOuterWindowIDs.Length()) {
-    return NS_ERROR_UNEXPECTED;
-  }
-
-  bool subFrame = aLoadInfo->GetExternalContentPolicyType() == nsIContentPolicy::TYPE_SUBDOCUMENT;
-  if (!aFrameAncestors.SetCapacity(subFrame ? size : size + 1, fallible)) {
-    return NS_ERROR_OUT_OF_MEMORY;
-  }
-
-  // The immediate parent is always the first element in the ancestor arrays, however
-  // SUBDOCUMENTs do not have their immediate parent included, so we inject it here.
-  // This will force wrapper.parentWindowId == wrapper.frameAncestors[0].frameId to
-  // always be true.  All ather requests already match this way.
-  if (subFrame) {
-    auto ancestor = aFrameAncestors.AppendElement();
-    GetDocumentURL(ancestor->mUrl);
-    ancestor->mFrameId = ParentWindowId();
-  }
-
-  for (uint32_t i = 0; i < size; ++i) {
-    auto ancestor = aFrameAncestors.AppendElement();
-    nsCOMPtr<nsIURI> uri;
-    MOZ_TRY(ancestorPrincipals[i]->GetURI(getter_AddRefs(uri)));
-    if (!uri) {
-      return NS_ERROR_UNEXPECTED;
-    }
-    MOZ_TRY(uri->GetSpec(ancestor->mUrl));
-    ancestor->mFrameId = NormalizeWindowID(aLoadInfo, ancestorOuterWindowIDs[i]);
-  }
-  return NS_OK;
-}
-
 /*****************************************************************************
  * ...
  *****************************************************************************/
 
 MozContentPolicyType
 GetContentPolicyType(uint32_t aType)
 {
   // Note: Please keep this function in sync with the external types in
@@ -648,17 +594,17 @@ ChannelWrapper::GetFinalURI(ErrorResult&
   nsresult rv = NS_ERROR_UNEXPECTED;
   nsCOMPtr<nsIURI> uri;
   if (nsCOMPtr<nsIChannel> chan = MaybeChannel()) {
     rv = NS_GetFinalChannelURI(chan, getter_AddRefs(uri));
   }
   if (NS_FAILED(rv)) {
     aRv.Throw(rv);
   }
-  return uri.forget();
+  return uri.forget();;
 }
 
 void
 ChannelWrapper::GetFinalURL(nsCString& aRetVal, ErrorResult& aRv) const
 {
   nsCOMPtr<nsIURI> uri = GetFinalURI(aRv);
   if (uri) {
     Unused << uri->GetSpec(aRetVal);

--- a/toolkit/components/extensions/webrequest/ChannelWrapper.h
+++ b/toolkit/components/extensions/webrequest/ChannelWrapper.h
@@ -148,18 +148,16 @@ public:
     }
     return nullptr;
   }
 
   int64_t WindowId() const;
 
   int64_t ParentWindowId() const;
 
-  void GetFrameAncestors(dom::Nullable<nsTArray<dom::MozFrameAncestorInfo>>& aFrameAncestors, ErrorResult& aRv) const;
-
   bool IsSystemLoad() const;
 
   void GetOriginURL(nsCString& aRetVal) const;
 
   void GetDocumentURL(nsCString& aRetVal) const;
 
   already_AddRefed<nsIURI> GetOriginURI() const;
 
@@ -173,16 +171,17 @@ public:
 
   bool GetCanModify(ErrorResult& aRv) const;
 
 
   void GetProxyInfo(dom::Nullable<dom::MozProxyInfo>& aRetVal, ErrorResult& aRv) const;
 
   void GetRemoteAddress(nsCString& aRetVal) const;
 
+
   void GetRequestHeaders(JSContext* cx, JS::MutableHandle<JSObject*> aRetVal, ErrorResult& aRv) const;
 
   void GetResponseHeaders(JSContext* cx, JS::MutableHandle<JSObject*> aRetVal, ErrorResult& aRv) const;
 
   void SetRequestHeader(const nsCString& header, const nsCString& value, ErrorResult& aRv);
 
   void SetResponseHeader(const nsCString& header, const nsCString& value, ErrorResult& aRv);
 
@@ -208,18 +207,16 @@ private:
       aRv.Throw(NS_ERROR_UNEXPECTED);
       return false;
     }
     return true;
   }
 
   uint64_t WindowId(nsILoadInfo* aLoadInfo) const;
 
-  nsresult GetFrameAncestors(nsILoadInfo* aLoadInfo, nsTArray<dom::MozFrameAncestorInfo>& aFrameAncestors) const;
-
   static uint64_t GetNextId()
   {
     static uint64_t sNextId = 1;
     return ++sNextId;
   }
 
   const uint64_t mId = GetNextId();
   nsCOMPtr<nsISupports> mParent;

--- a/toolkit/modules/addons/WebRequest.jsm
+++ b/toolkit/modules/addons/WebRequest.jsm
@@ -183,17 +183,17 @@ class ResponseHeaderChanger extends Head
 }
 
 const MAYBE_CACHED_EVENTS = new Set([
   "onResponseStarted", "onBeforeRedirect", "onCompleted", "onErrorOccurred",
 ]);
 
 const OPTIONAL_PROPERTIES = [
   "requestHeaders", "responseHeaders", "statusCode", "statusLine", "error", "redirectUrl",
-  "requestBody", "scheme", "realm", "isProxy", "challenger", "proxyInfo", "ip", "frameAncestors",
+  "requestBody", "scheme", "realm", "isProxy", "challenger", "proxyInfo", "ip",
 ];
 
 function serializeRequestData(eventName) {
   let data = {
     requestId: this.requestId,
     url: this.url,
     originUrl: this.originUrl,
     documentUrl: this.documentUrl,
@@ -732,23 +732,16 @@ HttpObserverManager = {
 
       ip: channel.remoteAddress,
 
       proxyInfo: channel.proxyInfo,
 
       serialize: serializeRequestData,
     };
 
-    try {
-      let {frameAncestors} = channel;
-      if (frameAncestors !== null) {
-        data.frameAncestors = frameAncestors;
-      }
-    } catch (e) {}
-
     // force the protocol to be ws again.
     if (data.type == "websocket" && data.url.startsWith("http")) {
       data.url = `ws${data.url.substring(4)}`;
     }
 
     return Object.assign(data, extraData);
   },
 

--- a/toolkit/modules/addons/WebRequestContent.js
+++ b/toolkit/modules/addons/WebRequestContent.js
@@ -113,17 +113,16 @@ var ContentPolicy = {
     }
 
     if (!ids.length) {
       return Ci.nsIContentPolicy.ACCEPT;
     }
 
     let windowId = 0;
     let parentWindowId = -1;
-    let frameAncestors = [];
     let mm = Services.cpmm;
 
     function getWindowId(window) {
       return window.QueryInterface(Ci.nsIInterfaceRequestor)
         .getInterface(Ci.nsIDOMWindowUtils)
         .outerWindowID;
     }
 
@@ -148,28 +147,16 @@ var ContentPolicy = {
           doc = node;
         }
         window = doc.defaultView;
       }
 
       windowId = getWindowId(window);
       if (window.parent !== window) {
         parentWindowId = getWindowId(window.parent);
-
-        for (let frame = window.parent; ; frame = frame.parent) {
-          frameAncestors.push({
-            url: frame.document.documentURIObject.spec,
-            frameId: getWindowId(frame),
-          });
-          if (frame === frame.parent) {
-            // Set the last frameId to zero for top level frame.
-            frameAncestors[frameAncestors.length - 1].frameId = 0;
-            break;
-          }
-        }
       }
 
       let ir = window.QueryInterface(Ci.nsIInterfaceRequestor)
                      .getInterface(Ci.nsIDocShell)
                      .QueryInterface(Ci.nsIInterfaceRequestor);
       try {
         // If e10s is disabled, this throws NS_NOINTERFACE for closed tabs.
         mm = ir.getInterface(Ci.nsIContentFrameMessageManager);
@@ -180,19 +167,16 @@ var ContentPolicy = {
       }
     }
 
     let data = {ids,
                 url,
                 type: WebRequestCommon.typeForPolicyType(policyType),
                 windowId,
                 parentWindowId};
-    if (frameAncestors.length > 0) {
-      data.frameAncestors = frameAncestors;
-    }
     if (requestOrigin) {
       data.originUrl = requestOrigin.spec;
     }
     mm.sendAsyncMessage("WebRequest:ShouldLoad", data);
 
     return Ci.nsIContentPolicy.ACCEPT;
   },
 

--- a/toolkit/modules/tests/browser/browser.ini
+++ b/toolkit/modules/tests/browser/browser.ini
@@ -30,15 +30,14 @@ support-files =
 [browser_FinderHighlighter.js]
 skip-if = debug || os = "linux"
 support-files = file_FinderSample.html
 [browser_Geometry.js]
 [browser_InlineSpellChecker.js]
 [browser_WebNavigation.js]
 skip-if = true # Superseded by WebExtension tests
 [browser_WebRequest.js]
-[browser_WebRequest_ancestors.js]
 [browser_WebRequest_cookies.js]
 [browser_WebRequest_filtering.js]
 [browser_PageMetadata.js]
 [browser_PromiseMessage.js]
 [browser_RemotePageManager.js]
 [browser_Troubleshoot.js]

--- a/toolkit/modules/tests/browser/browser_WebRequest.js
+++ b/toolkit/modules/tests/browser/browser_WebRequest.js
@@ -39,21 +39,16 @@ function onBeforeRequest(details) {
     is(details.browser, expected_browser, "correct <browser> element");
     checkType(details);
 
     windowIDs.set(details.url, details.windowId);
     if (details.url.indexOf("page2") != -1) {
       let page1id = windowIDs.get(URL);
       ok(details.windowId != page1id, "sub-frame gets its own window ID");
       is(details.parentWindowId, page1id, "parent window id is correct");
-
-      is(details.frameAncestors.length, 1, "correctly has only one ancestor");
-      let ancestor = details.frameAncestors[0];
-      ok(ancestor.url.includes("page1"), "parent window url seems correct");
-      is(ancestor.frameId, page1id, "parent window id is correct");
     }
   }
   if (details.url.indexOf("_bad.") != -1) {
     return {cancel: true};
   }
   return undefined;
 }
 

deleted file mode 100644
--- a/toolkit/modules/tests/browser/browser_WebRequest_ancestors.js
+++ /dev/null
@@ -1,54 +0,0 @@
-"use strict";
-
-var { interfaces: Ci, classes: Cc, utils: Cu, results: Cr } = Components;
-
-Cu.importGlobalProperties(["XMLHttpRequest"]);
-
-var {WebRequest} = Cu.import("resource://gre/modules/WebRequest.jsm", {});
-var {PromiseUtils} = Cu.import("resource://gre/modules/PromiseUtils.jsm", {});
-
-add_task(async function test_ancestors_exist() {
-  let deferred = PromiseUtils.defer();
-  function onBeforeRequest(details) {
-    info(`onBeforeRequest ${details.url}`);
-    ok(typeof details.frameAncestors === "object", `ancestors exists [${typeof details.frameAncestors}]`);
-    deferred.resolve();
-  }
-
-  WebRequest.onBeforeRequest.addListener(onBeforeRequest, {urls: new MatchPatternSet(["http://mochi.test/*"])}, ["blocking"]);
-
-  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, "http://mochi.test:8888/");
-  await deferred.promise;
-  await BrowserTestUtils.removeTab(tab);
-
-  WebRequest.onBeforeRequest.removeListener(onBeforeRequest);
-});
-
-add_task(async function test_ancestors_null() {
-  let deferred = PromiseUtils.defer();
-  function onBeforeRequest(details) {
-    info(`onBeforeRequest ${details.url}`);
-    ok(details.frameAncestors === undefined, "ancestors do not exist");
-    deferred.resolve();
-  }
-
-  WebRequest.onBeforeRequest.addListener(onBeforeRequest, null, ["blocking"]);
-
-  function fetch(url) {
-    return new Promise((resolve, reject) => {
-      let xhr = new XMLHttpRequest();
-      xhr.mozBackgroundRequest = true;
-      xhr.open("GET", url);
-      xhr.onload = () => { resolve(xhr.responseText); };
-      xhr.onerror = () => { reject(xhr.status); };
-      // use a different contextId to avoid auth cache.
-      xhr.setOriginAttributes({userContextId: 1});
-      xhr.send();
-    });
-  }
-
-  await fetch("http://mochi.test:8888/");
-  await deferred.promise;
-
-  WebRequest.onBeforeRequest.removeListener(onBeforeRequest);
-});