Backed out changeset 88337b6e4e3e (bug 1666881) for causing failures regarding the fission.autostart pref.

CLOSED TREE
2020-09-24 15:41:33 +03:00 · 2020-09-24 15:41:33 +03:00 · 8b9238686c
--- a/docshell/base/BrowsingContext.cpp
+++ b/docshell/base/BrowsingContext.cpp
@ -414,7 +414,7 @@ void BrowsingContext::CreateFromIPC(BrowsingContext::IPCInitializer&& aInit,
  context->mCreatedDynamically = aInit.mCreatedDynamically;
  if (context->GetHasSessionHistory()) {
    context->CreateChildSHistory();
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      context->GetChildSessionHistory()->SetIndexAndLength(
          aInit.mSessionHistoryIndex, aInit.mSessionHistoryCount, nsID());
    }
@ -2084,8 +2084,7 @@ BrowsingContext::IPCInitializer BrowsingContext::GetIPCInitializer() {
  init.mUseRemoteSubframes = mUseRemoteSubframes;
  init.mCreatedDynamically = mCreatedDynamically;
  init.mOriginAttributes = mOriginAttributes;
-  if (mChildSessionHistory &&
-      StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (mChildSessionHistory && StaticPrefs::fission_sessionHistoryInParent()) {
    init.mSessionHistoryIndex = mChildSessionHistory->Index();
    init.mSessionHistoryCount = mChildSessionHistory->Count();
  }
@ -2583,7 +2582,7 @@ void BrowsingContext::InitSessionHistory() {
 }

 ChildSHistory* BrowsingContext::GetChildSessionHistory() {
-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (!StaticPrefs::fission_sessionHistoryInParent()) {
    // For now we're checking that the session history object for the child
    // process is available before returning the ChildSHistory object, because
    // it is the actual implementation that ChildSHistory forwards to. This can
@ -2641,8 +2640,7 @@ bool BrowsingContext::CanSet(FieldIndex<IDX_PendingInitialization>,

 void BrowsingContext::SessionHistoryChanged(int32_t aIndexDelta,
                                            int32_t aLengthDelta) {
-  if (XRE_IsParentProcess() ||
-      StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (XRE_IsParentProcess() || StaticPrefs::fission_sessionHistoryInParent()) {
    // This method is used to test index and length for the session history
    // in child process only.
    return;
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@ -834,7 +834,7 @@ nsresult nsDocShell::LoadURI(nsDocShellLoadState* aLoadState,
    MOZ_LOG(gSHLog, LogLevel::Debug,
            ("nsDocShell[%p]: loading from session history", this));

-    if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (!StaticPrefs::fission_sessionHistoryInParent()) {
      return LoadHistoryEntry(aLoadState->SHEntry(), aLoadState->LoadType());
    }

@ -929,7 +929,7 @@ bool nsDocShell::MaybeHandleSubframeHistory(
  parentDS->GetLoadType(&parentLoadType);

  if (!aContinueHandlingSubframeHistory) {
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      if (nsDocShell::Cast(parentDS.get())->IsLoadingFromSessionHistory() &&
          !GetCreatedDynamically()) {
        if (XRE_IsContentProcess()) {
@ -1150,7 +1150,7 @@ void nsDocShell::FirePageHideNotificationInternal(
        MOZ_LOG(
            gSHLog, LogLevel::Debug,
            ("document %p unloading, remove dynamic subframe entries", this));
-        if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+        if (StaticPrefs::fission_sessionHistoryInParent()) {
          if (mActiveEntry) {
            mBrowsingContext->RemoveDynEntriesFromActiveSessionHistoryEntry();
          }
@ -1408,7 +1408,7 @@ bool nsDocShell::SetCurrentURI(nsIURI* aURI, nsIRequest* aRequest,
  bool isRoot = mBrowsingContext->IsTop();
  bool isSubFrame = false;  // Is this a subframe navigation?

-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (mLoadingEntry) {
      isSubFrame = mLoadingEntry->mInfo.IsSubFrame();
      MOZ_LOG(gSHLog, LogLevel::Debug,
@ -2724,7 +2724,7 @@ void nsDocShell::StoreWindowNameToSHEntries() {
        mOSHE, [&](nsISHEntry* aEntry) { aEntry->SetName(name); });
  }

-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (XRE_IsParentProcess()) {
      SessionHistoryEntry* entry =
          mBrowsingContext->Canonical()->GetActiveSessionHistoryEntry();
@ -3055,7 +3055,7 @@ nsresult nsDocShell::AddChildSHEntry(nsISHEntry* aCloneRef,
                                     nsISHEntry* aNewEntry,
                                     int32_t aChildOffset, uint32_t aLoadType,
                                     bool aCloneChildren) {
-  MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+  MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());
  nsresult rv = NS_OK;

  if (mLSHE && aLoadType != LOAD_PUSHSTATE) {
@ -3083,7 +3083,7 @@ nsresult nsDocShell::AddChildSHEntry(nsISHEntry* aCloneRef,
 nsresult nsDocShell::AddChildSHEntryToParent(nsISHEntry* aNewEntry,
                                             int32_t aChildOffset,
                                             bool aCloneChildren) {
-  MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+  MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());
  /* You will get here when you are in a subframe and
   * a new url has been loaded on you.
   * The mOSHE in this subframe will be the previous url's
@ -3244,7 +3244,7 @@ nsDocShell::GetDeviceSizeIsPageSize(bool* aValue) {
 }

 void nsDocShell::ClearFrameHistory(nsISHEntry* aEntry) {
-  MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+  MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());
  RefPtr<ChildSHistory> rootSH = GetRootSessionHistory();
  if (!rootSH || !aEntry) {
    return;
@ -3984,7 +3984,7 @@ nsresult nsDocShell::LoadErrorPage(nsIURI* aErrorURI, nsIURI* aFailedURI,
    // identifier, the error page won't persist.
    mLSHE->AbandonBFCacheEntry();
  }
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    // Commit the loading entry for the real load here, Embed will not commit
    // the loading entry for the error page. History will then contain an entry
    // for the real load, and the error page won't persist if we try loading
@ -4020,7 +4020,7 @@ nsDocShell::Reload(uint32_t aReloadFlags) {
  // Send notifications to the HistoryListener if any, about the impending
  // reload
  RefPtr<ChildSHistory> rootSH = GetRootSessionHistory();
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    MOZ_LOG(gSHLog, LogLevel::Debug, ("document %p Reload", this));
    bool forceReload = IsForceReloadType(loadType);
    if (!XRE_IsParentProcess()) {
@ -4286,7 +4286,7 @@ nsDocShell::LoadPageAsViewSource(nsIDocShell* aOtherDocShell,
  RefPtr<nsDocShellLoadState> loadState;
  uint32_t cacheKey;
  auto* otherDocShell = nsDocShell::Cast(aOtherDocShell);
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    loadState = new nsDocShellLoadState(newURI);
    if (!otherDocShell->FillLoadStateFromCurrentEntry(*loadState)) {
      return NS_ERROR_INVALID_POINTER;
@ -4344,7 +4344,7 @@ nsDocShell::GetCurrentDescriptor(nsISupports** aPageDescriptor) {
 already_AddRefed<nsIInputStream> nsDocShell::GetPostDataFromCurrentEntry()
    const {
  nsCOMPtr<nsIInputStream> postData;
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (mActiveEntry) {
      postData = mActiveEntry->GetPostData();
    } else if (mLoadingEntry) {
@ -4362,7 +4362,7 @@ already_AddRefed<nsIInputStream> nsDocShell::GetPostDataFromCurrentEntry()
 }

 Maybe<uint32_t> nsDocShell::GetCacheKeyFromCurrentEntry() const {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (mActiveEntry) {
      return Some(mActiveEntry->GetCacheKey());
    }
@ -5685,8 +5685,8 @@ nsresult nsDocShell::Embed(nsIContentViewer* aContentViewer,
  NS_ENSURE_SUCCESS(rv, rv);

  // XXX What if SetupNewViewer fails?
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ? !!mLoadingEntry
-                                                              : !!mLSHE) {
+  if (StaticPrefs::fission_sessionHistoryInParent() ? !!mLoadingEntry
+                                                    : !!mLSHE) {
    // Set history.state
    SetDocCurrentStateObj(mLSHE,
                          mLoadingEntry ? &mLoadingEntry->mInfo : nullptr);
@ -5702,7 +5702,7 @@ nsresult nsDocShell::Embed(nsIContentViewer* aContentViewer,
  }

  if (!aIsTransientAboutBlank &&
-      StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+      StaticPrefs::fission_sessionHistoryInParent()) {
    MOZ_LOG(gSHLog, LogLevel::Debug, ("document %p Embed", this));
    MoveLoadingToActiveEntry(mLoadType != LOAD_ERROR_PAGE);
  }
@ -7005,7 +7005,7 @@ nsresult nsDocShell::CaptureState() {
  if (MOZ_UNLIKELY(MOZ_LOG_TEST(gPageCacheLog, LogLevel::Debug))) {
    nsAutoCString spec;
    nsCOMPtr<nsIURI> uri;
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      uri = mActiveEntry->GetURI();
    } else {
      uri = mOSHE->GetURI();
@ -7327,7 +7327,7 @@ nsresult nsDocShell::RestoreFromHistory() {
  RefPtr<ChildSHistory> rootSH = GetRootSessionHistory();
  if (rootSH) {
    mPreviousEntryIndex = rootSH->Index();
-    if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (!StaticPrefs::fission_sessionHistoryInParent()) {
      rootSH->LegacySHistory()->UpdateIndex();
    }
    mLoadedEntryIndex = rootSH->Index();
@ -7856,8 +7856,7 @@ nsresult nsDocShell::CreateContentViewer(const nsACString& aContentType,
    // Be sure to have a correct mLSHE, it may have been cleared by
    // EndPageLoad. See bug 302115.
    ChildSHistory* shistory = GetSessionHistory();
-    if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup() && shistory &&
-        !mLSHE) {
+    if (!StaticPrefs::fission_sessionHistoryInParent() && shistory && !mLSHE) {
      int32_t idx = shistory->LegacySHistory()->GetRequestedIndex();
      if (idx == -1) {
        idx = shistory->Index();
@ -8197,7 +8196,7 @@ void nsDocShell::SetDocCurrentStateObj(nsISHEntry* aShEntry,
  NS_ENSURE_TRUE_VOID(document);

  nsCOMPtr<nsIStructuredCloneContainer> scContainer;
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    // If aInfo is null, just set the document's state object to null.
    if (aInfo) {
      scContainer = aInfo->GetStateData();
@ -8625,7 +8624,7 @@ bool nsDocShell::IsSameDocumentNavigation(nsDocShellLoadState* aLoadState,
    }
  }

-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (mActiveEntry && aLoadState->LoadIsFromSessionHistory()) {
      aState.mHistoryNavBetweenSameDoc = mActiveEntry->SharesDocumentWith(
          aLoadState->GetLoadingSessionHistoryInfo()->mInfo);
@ -8645,7 +8644,7 @@ bool nsDocShell::IsSameDocumentNavigation(nsDocShellLoadState* aLoadState,
 #ifdef DEBUG
  if (aState.mHistoryNavBetweenSameDoc) {
    nsCOMPtr<nsIInputStream> currentPostData;
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      currentPostData = mActiveEntry->GetPostData();
    } else {
      currentPostData = mOSHE->GetPostData();
@ -8669,7 +8668,7 @@ bool nsDocShell::IsSameDocumentNavigation(nsDocShellLoadState* aLoadState,
  // The restriction that the SHEntries in (a) must be different ensures
  // that history.go(0) and the like trigger full refreshes, rather than
  // same document navigations.
-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (!StaticPrefs::fission_sessionHistoryInParent()) {
    bool doSameDocumentNavigation =
        (aState.mHistoryNavBetweenSameDoc && mOSHE != aLoadState->SHEntry()) ||
        (!aLoadState->SHEntry() && !aLoadState->PostDataStream() &&
@ -8746,9 +8745,9 @@ nsresult nsDocShell::HandleSameDocumentNavigation(
  nsCOMPtr<nsIPrincipal> newURITriggeringPrincipal, newURIPrincipalToInherit,
      newURIPartitionedPrincipalToInherit;
  nsCOMPtr<nsIContentSecurityPolicy> newCsp;
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ? !!mActiveEntry
-                                                              : !!mOSHE) {
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent() ? !!mActiveEntry
+                                                    : !!mOSHE) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      newURITriggeringPrincipal = mActiveEntry->GetTriggeringPrincipal();
      newURIPrincipalToInherit = mActiveEntry->GetPrincipalToInherit();
      newURIPartitionedPrincipalToInherit =
@ -8783,9 +8782,9 @@ nsresult nsDocShell::HandleSameDocumentNavigation(
  uint32_t cacheKey = 0;

  bool scrollRestorationIsManual = false;
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ? !!mActiveEntry
-                                                              : !!mOSHE) {
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent() ? !!mActiveEntry
+                                                    : !!mOSHE) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      // FIXME Need to set scroll position on mActiveEntry.
      scrollRestorationIsManual = mActiveEntry->GetScrollRestorationIsManual();
    } else {
@ -8800,7 +8799,7 @@ nsresult nsDocShell::HandleSameDocumentNavigation(
    // above -- it filters out some LOAD_CMD_NORMAL cases that we
    // wouldn't want here.
    if (aLoadState->LoadType() & LOAD_CMD_NORMAL) {
-      if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+      if (StaticPrefs::fission_sessionHistoryInParent()) {
        postData = mActiveEntry->GetPostData();
        cacheKey = mActiveEntry->GetCacheKey();
      } else {
@ -8833,7 +8832,7 @@ nsresult nsDocShell::HandleSameDocumentNavigation(

  // If we're doing a history load, use its scroll restoration state.
  if (aLoadState->LoadIsFromSessionHistory()) {
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      scrollRestorationIsManual = aLoadState->GetLoadingSessionHistoryInfo()
                                      ->mInfo.GetScrollRestorationIsManual();
    } else {
@ -8864,8 +8863,7 @@ nsresult nsDocShell::HandleSameDocumentNavigation(
      SetCacheKeyOnHistoryEntry(mOSHE, cacheKey);
    }
  }
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() &&
-      mLoadingEntry) {
+  if (StaticPrefs::fission_sessionHistoryInParent() && mLoadingEntry) {
    MOZ_LOG(
        gSHLog, LogLevel::Debug,
        ("Moving the loading entry to the active entry on nsDocShell %p to %s",
@ -8935,13 +8933,13 @@ nsresult nsDocShell::HandleSameDocumentNavigation(
  nscoord bx = 0;
  nscoord by = 0;
  bool needsScrollPosUpdate = false;
-  if ((StaticPrefs::fission_sessionHistoryInParent_AtStartup() ? !!mActiveEntry
-                                                               : !!mOSHE) &&
+  if ((StaticPrefs::fission_sessionHistoryInParent() ? !!mActiveEntry
+                                                     : !!mOSHE) &&
      (aLoadState->LoadType() == LOAD_HISTORY ||
       aLoadState->LoadType() == LOAD_RELOAD_NORMAL) &&
      !scrollRestorationIsManual) {
    needsScrollPosUpdate = true;
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      mActiveEntry->GetScrollPosition(&bx, &by);
    } else {
      mOSHE->GetScrollPosition(&bx, &by);
@ -9259,7 +9257,7 @@ nsresult nsDocShell::InternalLoad(nsDocShellLoadState* aLoadState,
    SetHistoryEntryAndUpdateBC(Some<nsISHEntry*>(aLoadState->SHEntry()),
                               Nothing());
    if (aLoadState->LoadIsFromSessionHistory() &&
-        !StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+        !StaticPrefs::fission_sessionHistoryInParent()) {
      // We're making history navigation or a reload. Make sure our history ID
      // points to the same ID as SHEntry's docshell ID.
      nsID historyID = {};
@ -9285,7 +9283,7 @@ nsresult nsDocShell::InternalLoad(nsDocShellLoadState* aLoadState,
    if (shistory) {
      shistory->RemovePendingHistoryNavigations();
    }
-    if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (!StaticPrefs::fission_sessionHistoryInParent()) {
      // It's possible that the previous viewer of mContentViewer is the
      // viewer that will end up in aLoadState->SHEntry() when it gets closed.
      // If that's the case, we need to go ahead and force it into its shentry
@ -10087,7 +10085,7 @@ nsresult nsDocShell::DoURILoad(nsDocShellLoadState* aLoadState,
  uint32_t cacheKey = 0;
  if (aCacheKey) {
    cacheKey = *aCacheKey;
-  } else if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  } else if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (mLoadingEntry) {
      cacheKey = mLoadingEntry->mInfo.GetCacheKey();
    } else if (mActiveEntry) {  // for reload cases
@ -10658,8 +10656,8 @@ bool nsDocShell::OnNewURI(nsIURI* aURI, nsIChannel* aChannel,
   * Hopefully I don't have to do that.
   */
  if (equalUri &&
-      (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ? !!mActiveEntry
-                                                               : !!mOSHE) &&
+      (StaticPrefs::fission_sessionHistoryInParent() ? !!mActiveEntry
+                                                     : !!mOSHE) &&
      (mLoadType == LOAD_NORMAL || mLoadType == LOAD_LINK ||
       mLoadType == LOAD_STOP_CONTENT) &&
      !inputStream) {
@ -10693,14 +10691,14 @@ bool nsDocShell::OnNewURI(nsIURI* aURI, nsIChannel* aChannel,

    SetCacheKeyOnHistoryEntry(mLSHE ? mLSHE : mOSHE, cacheKey);

-    if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (!StaticPrefs::fission_sessionHistoryInParent()) {
      // Since we're force-reloading, clear all the sub frame history.
      ClearFrameHistory(mLSHE);
      ClearFrameHistory(mOSHE);
    }
  }

-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (!StaticPrefs::fission_sessionHistoryInParent()) {
    // Clear subframe history on refresh.
    // XXX: history.go(0) won't go this path as aLoadType is LOAD_HISTORY in
    // this case. One should re-validate after bug 1331865 fixed.
@ -10750,11 +10748,11 @@ bool nsDocShell::OnNewURI(nsIURI* aURI, nsIChannel* aChannel,
  // If this was a history load or a refresh, or it was a history load but
  // later changed to LOAD_NORMAL_REPLACE due to redirection, update the index
  // in session history.
-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup() && rootSH &&
+  if (!StaticPrefs::fission_sessionHistoryInParent() && rootSH &&
      ((mLoadType & (LOAD_CMD_HISTORY | LOAD_CMD_RELOAD)) ||
       mLoadType == LOAD_NORMAL_REPLACE)) {
    mPreviousEntryIndex = rootSH->Index();
-    if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (!StaticPrefs::fission_sessionHistoryInParent()) {
      rootSH->LegacySHistory()->UpdateIndex();
    }
    mLoadedEntryIndex = rootSH->Index();
@ -11000,7 +10998,7 @@ nsresult nsDocShell::UpdateURLAndHistory(Document* aDocument, nsIURI* aNewURI,
  aNewURI->EqualsExceptRef(aCurrentURI, &sameExceptHashes);
  bool uriWasModified;
  if (sameExceptHashes) {
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      uriWasModified = mActiveEntry && mActiveEntry->GetURIWasModified();
    } else {
      uriWasModified = oldOSHE && oldOSHE->GetURIWasModified();
@ -11025,7 +11023,7 @@ nsresult nsDocShell::UpdateURLAndHistory(Document* aDocument, nsIURI* aNewURI,
    nsPoint scrollPos = GetCurScrollPos();

    bool scrollRestorationIsManual;
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      // FIXME Need to save the current scroll position on mActiveEntry.
      scrollRestorationIsManual = mActiveEntry->GetScrollRestorationIsManual();
    } else {
@ -11037,7 +11035,7 @@ nsresult nsDocShell::UpdateURLAndHistory(Document* aDocument, nsIURI* aNewURI,

    nsCOMPtr<nsIContentSecurityPolicy> csp = aDocument->GetCsp();

-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      MOZ_LOG(gSHLog, LogLevel::Debug,
              ("document %p UpdateActiveEntry replace", this));
      nsString title(mActiveEntry->GetTitle());
@ -11077,7 +11075,7 @@ nsresult nsDocShell::UpdateURLAndHistory(Document* aDocument, nsIURI* aNewURI,
      // we'll just set mOSHE here.
      mOSHE = newSHEntry;
    }
-  } else if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  } else if (StaticPrefs::fission_sessionHistoryInParent()) {
    MOZ_LOG(gSHLog, LogLevel::Debug,
            ("document %p UpdateActiveEntry non-replace", this));
    UpdateActiveEntry(
@ -11110,7 +11108,7 @@ nsresult nsDocShell::UpdateURLAndHistory(Document* aDocument, nsIURI* aNewURI,
    newSHEntry->SetLoadReplace(false);
  }

-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (!StaticPrefs::fission_sessionHistoryInParent()) {
    // Step 2.4 and 3: Modify new/original session history entry and clear its
    // POST data, if there is any.
    newSHEntry->SetStateData(aData);
@ -11177,7 +11175,7 @@ nsresult nsDocShell::UpdateURLAndHistory(Document* aDocument, nsIURI* aNewURI,

 NS_IMETHODIMP
 nsDocShell::GetCurrentScrollRestorationIsManual(bool* aIsManual) {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    *aIsManual = mActiveEntry && mActiveEntry->GetScrollRestorationIsManual();
    return NS_OK;
  }
@ -11285,8 +11283,7 @@ nsresult nsDocShell::AddToSessionHistory(
    nsISHEntry** aNewEntry) {
  MOZ_ASSERT(aURI, "uri is null");
  MOZ_ASSERT(!aChannel || !aTriggeringPrincipal, "Shouldn't have both set");
-  MOZ_DIAGNOSTIC_ASSERT(
-      !StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+  MOZ_DIAGNOSTIC_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());

 #if defined(DEBUG)
  if (MOZ_LOG_TEST(gDocShellLog, LogLevel::Debug)) {
@ -11504,7 +11501,7 @@ void nsDocShell::UpdateActiveEntry(
    nsIContentSecurityPolicy* aCsp, const nsAString& aTitle,
    const Maybe<bool>& aScrollRestorationIsManual,
    nsIStructuredCloneContainer* aData, bool aURIWasModified) {
-  MOZ_ASSERT(StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+  MOZ_ASSERT(StaticPrefs::fission_sessionHistoryInParent());
  MOZ_ASSERT(aURI, "uri is null");
  MOZ_ASSERT(mLoadType == LOAD_PUSHSTATE,
             "This code only deals with pushState");
@ -11650,10 +11647,10 @@ NS_IMETHODIMP
 nsDocShell::PersistLayoutHistoryState() {
  nsresult rv = NS_OK;

-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ? !!mActiveEntry
-                                                              : !!mOSHE) {
+  if (StaticPrefs::fission_sessionHistoryInParent() ? !!mActiveEntry
+                                                    : !!mOSHE) {
    bool scrollRestorationIsManual;
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      scrollRestorationIsManual = mActiveEntry->GetScrollRestorationIsManual();
    } else {
      scrollRestorationIsManual = mOSHE->GetScrollRestorationIsManual();
@ -12101,7 +12098,7 @@ nsDocShell::GetIsExecutingOnLoadHandler(bool* aResult) {
 NS_IMETHODIMP
 nsDocShell::GetLayoutHistoryState(nsILayoutHistoryState** aLayoutHistoryState) {
  nsCOMPtr<nsILayoutHistoryState> state;
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (mActiveEntry) {
      state = mActiveEntry->GetLayoutHistoryState();
    }
@ -12804,7 +12801,7 @@ nsDocShell::ResumeRedirectedLoad(uint64_t aIdentifier, int32_t aHistoryIndex) {
        // If we're performing a history load, locate the correct history entry,
        // and set the relevant bits on our loadState.
        if (aHistoryIndex >= 0 && self->GetSessionHistory() &&
-            !StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+            !StaticPrefs::fission_sessionHistoryInParent()) {
          nsCOMPtr<nsISHistory> legacySHistory =
              self->GetSessionHistory()->LegacySHistory();

@ -13197,7 +13194,7 @@ void nsDocShell::SetLoadingSessionHistoryInfo(
 }

 void nsDocShell::MoveLoadingToActiveEntry(bool aCommit) {
-  MOZ_ASSERT(StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+  MOZ_ASSERT(StaticPrefs::fission_sessionHistoryInParent());

  MOZ_LOG(gSHLog, LogLevel::Debug,
          ("nsDocShell %p MoveLoadingToActiveEntry", this));
--- a/docshell/shistory/ChildSHistory.cpp
+++ b/docshell/shistory/ChildSHistory.cpp
@ -33,7 +33,7 @@ void ChildSHistory::SetIsInProcess(bool aIsInProcess) {
    return;
  }

-  if (mHistory || StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (mHistory || StaticPrefs::fission_sessionHistoryInParent()) {
    return;
  }

@ -41,15 +41,14 @@ void ChildSHistory::SetIsInProcess(bool aIsInProcess) {
 }

 int32_t ChildSHistory::Count() {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ||
-      mAsyncHistoryLength) {
+  if (StaticPrefs::fission_sessionHistoryInParent() || mAsyncHistoryLength) {
    uint32_t length = mLength;
    for (uint32_t i = 0; i < mPendingSHistoryChanges.Length(); ++i) {
      length += mPendingSHistoryChanges[i].mLengthDelta;
    }

    if (mAsyncHistoryLength) {
-      MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+      MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());
      // XXX The assertion may be too strong here, but it fires only
      //    when the pref is enabled.
      MOZ_ASSERT(mHistory->GetCount() == int32_t(length));
@ -60,15 +59,14 @@ int32_t ChildSHistory::Count() {
 }

 int32_t ChildSHistory::Index() {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() ||
-      mAsyncHistoryLength) {
+  if (StaticPrefs::fission_sessionHistoryInParent() || mAsyncHistoryLength) {
    uint32_t index = mIndex;
    for (uint32_t i = 0; i < mPendingSHistoryChanges.Length(); ++i) {
      index += mPendingSHistoryChanges[i].mIndexDelta;
    }

    if (mAsyncHistoryLength) {
-      MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+      MOZ_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());
      int32_t realIndex;
      mHistory->GetIndex(&realIndex);
      // XXX The assertion may be too strong here, but it fires only
@ -108,7 +106,7 @@ void ChildSHistory::SetIndexAndLength(uint32_t aIndex, uint32_t aLength,
 }

 void ChildSHistory::Reload(uint32_t aReloadFlags, ErrorResult& aRv) {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    if (XRE_IsParentProcess()) {
      nsISHistory* shistory =
          mBrowsingContext->Canonical()->GetSessionHistory();
@ -152,7 +150,7 @@ void ChildSHistory::Go(int32_t aOffset, bool aRequireUserInteraction,
    }

    // See Bug 1650095.
-    if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+    if (StaticPrefs::fission_sessionHistoryInParent()) {
      break;
    }

@ -190,7 +188,7 @@ void ChildSHistory::AsyncGo(int32_t aOffset, bool aRequireUserInteraction,
 }

 void ChildSHistory::GotoIndex(int32_t aIndex, ErrorResult& aRv) {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    nsCOMPtr<nsISHistory> shistory = mHistory;
    mBrowsingContext->HistoryGo(aIndex, [shistory](int32_t&& aRequestedIndex) {
      // FIXME Should probably only do this for non-fission.
@ -208,13 +206,13 @@ void ChildSHistory::RemovePendingHistoryNavigations() {
 }

 void ChildSHistory::EvictLocalContentViewers() {
-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (!StaticPrefs::fission_sessionHistoryInParent()) {
    mHistory->EvictAllContentViewers();
  }
 }

 nsISHistory* ChildSHistory::GetLegacySHistory(ErrorResult& aError) {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    aError.ThrowTypeError(
        "legacySHistory is not available with session history in the parent.");
    return nullptr;
@ -251,7 +249,7 @@ nsISupports* ChildSHistory::GetParentObject() const {
 }

 void ChildSHistory::SetAsyncHistoryLength(bool aEnable, ErrorResult& aRv) {
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() || !mHistory) {
+  if (StaticPrefs::fission_sessionHistoryInParent() || !mHistory) {
    aRv.Throw(NS_ERROR_FAILURE);
    return;
  }
--- a/docshell/shistory/nsSHistory.cpp
+++ b/docshell/shistory/nsSHistory.cpp
@ -329,7 +329,7 @@ uint32_t nsSHistory::CalcMaxTotalViewers() {
 // static
 void nsSHistory::UpdatePrefs() {
  Preferences::GetInt(PREF_SHISTORY_SIZE, &gHistoryMaxSize);
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    sHistoryMaxTotalViewers = 0;
    return;
  }
@ -430,7 +430,7 @@ nsresult nsSHistory::WalkHistoryEntries(nsISHEntry* aRootEntry,
        // If the SH pref is on and we are in the parent process, update
        // canonical BC directly
        bool foundChild = false;
-        if (StaticPrefs::fission_sessionHistoryInParent_AtStartup() &&
+        if (StaticPrefs::fission_sessionHistoryInParent() &&
            XRE_IsParentProcess()) {
          if (child->Canonical()->HasHistoryEntry(childEntry)) {
            childBC = child;
@ -681,7 +681,7 @@ nsresult nsSHistory::SetChildHistoryEntry(nsISHEntry* aEntry,
 void nsSHistory::HandleEntriesToSwapInDocShell(
    mozilla::dom::BrowsingContext* aBC, nsISHEntry* aOldEntry,
    nsISHEntry* aNewEntry) {
-  bool shPref = StaticPrefs::fission_sessionHistoryInParent_AtStartup();
+  bool shPref = StaticPrefs::fission_sessionHistoryInParent();
  if (aBC->IsInProcess() || !shPref) {
    nsDocShell* docshell = static_cast<nsDocShell*>(aBC->GetDocShell());
    if (docshell) {
@ -1825,7 +1825,7 @@ void nsSHistory::InitiateLoad(nsISHEntry* aFrameEntry,
  // a same-document navigation (see nsDocShell::IsSameDocumentNavigation), so
  // record that here in the LoadingSessionHistoryEntry.
  bool loadingFromActiveEntry;
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    loadingFromActiveEntry =
        aFrameBC->Canonical()->GetActiveSessionHistoryEntry() == aFrameEntry;
  } else {
@ -1836,7 +1836,7 @@ void nsSHistory::InitiateLoad(nsISHEntry* aFrameEntry,
  loadState->SetLoadIsFromSessionHistory(mRequestedIndex, Length(),
                                         loadingFromActiveEntry);

-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    nsCOMPtr<SessionHistoryEntry> she = do_QueryInterface(aFrameEntry);
    aFrameBC->Canonical()->AddLoadingSessionHistoryEntry(
        loadState->GetLoadingSessionHistoryInfo()->mLoadId, she);
@ -1861,8 +1861,7 @@ void nsSHistory::InitiateLoad(nsISHEntry* aFrameEntry,
 NS_IMETHODIMP
 nsSHistory::CreateEntry(nsISHEntry** aEntry) {
  nsCOMPtr<nsISHEntry> entry;
-  if (XRE_IsParentProcess() &&
-      StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (XRE_IsParentProcess() && StaticPrefs::fission_sessionHistoryInParent()) {
    entry = new SessionHistoryEntry();
  } else {
    entry = new nsSHEntry();
--- a/dom/base/nsCCUncollectableMarker.cpp
+++ b/dom/base/nsCCUncollectableMarker.cpp
@ -251,8 +251,7 @@ void MarkDocShell(nsIDocShellTreeItem* aNode, bool aCleanupJS) {
  nsISHistory* legacyHistory =
      history ? history->GetLegacySHistory(ignore) : nullptr;
  if (legacyHistory) {
-    MOZ_DIAGNOSTIC_ASSERT(
-        !StaticPrefs::fission_sessionHistoryInParent_AtStartup());
+    MOZ_DIAGNOSTIC_ASSERT(!StaticPrefs::fission_sessionHistoryInParent());
    int32_t historyCount = history->Count();
    for (int32_t i = 0; i < historyCount; ++i) {
      nsCOMPtr<nsISHEntry> shEntry;
--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@ -1873,7 +1873,7 @@ void nsFrameLoader::StartDestroy(bool aForProcessSwitch) {
      RefPtr<ChildSHistory> childSHistory =
          browsingContext->Top()->GetChildSessionHistory();
      if (childSHistory) {
-        if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+        if (StaticPrefs::fission_sessionHistoryInParent()) {
          browsingContext->RemoveFromSessionHistory();
        } else {
          AutoTArray<nsID, 16> ids({browsingContext->GetHistoryID()});
--- a/dom/base/nsGlobalWindowOuter.cpp
+++ b/dom/base/nsGlobalWindowOuter.cpp
@ -6348,7 +6348,7 @@ bool nsGlobalWindowOuter::IsOnlyTopLevelDocumentInSHistory() {
  // Disabled since IsFrame() is buggy in Fission
  // MOZ_ASSERT(mBrowsingContext->IsTop());

-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    return mBrowsingContext->GetIsSingleToplevelInHistory();
  }

--- a/dom/ipc/BrowserChild.cpp
+++ b/dom/ipc/BrowserChild.cpp
@ -3450,7 +3450,7 @@ nsresult BrowserChild::CanCancelContentJS(

  // If we have session history in the parent we've already performed
  // the checks following, so we can return early.
-  if (StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (StaticPrefs::fission_sessionHistoryInParent()) {
    *aCanCancel = true;
    return NS_OK;
  }
--- a/dom/ipc/BrowserParent.cpp
+++ b/dom/ipc/BrowserParent.cpp
@ -3519,7 +3519,7 @@ bool BrowserParent::CanCancelContentJS(
    nsIURI* aNavigationURI) const {
  // Pre-checking if we can cancel content js in the parent is only
  // supported when session history in the parent is enabled.
-  if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (!StaticPrefs::fission_sessionHistoryInParent()) {
    // If session history in the parent isn't enabled, this check will
    // be fully done in BrowserChild::CanCancelContentJS
    return true;
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@ -2060,7 +2060,7 @@ nsDocumentViewer::Show(void) {
      treeItem->GetInProcessSameTypeRootTreeItem(getter_AddRefs(root));
      nsCOMPtr<nsIWebNavigation> webNav = do_QueryInterface(root);
      RefPtr<ChildSHistory> history = webNav->GetSessionHistory();
-      if (!StaticPrefs::fission_sessionHistoryInParent_AtStartup() && history) {
+      if (!StaticPrefs::fission_sessionHistoryInParent() && history) {
        int32_t prevIndex, loadedIndex;
        nsCOMPtr<nsIDocShell> docShell = do_QueryInterface(treeItem);
        docShell->GetPreviousEntryIndex(&prevIndex);
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@ -3590,7 +3590,7 @@
 - name: fission.sessionHistoryInParent
  type: bool
  value: false
-  mirror: once
+  mirror: always

 # Allow renaming of process names to the origin on nightly
 # Setting this pref creates a privacy leak, but helps greatly with
--- a/netwerk/ipc/DocumentLoadListener.cpp
+++ b/netwerk/ipc/DocumentLoadListener.cpp
@ -626,8 +626,7 @@ auto DocumentLoadListener::Open(nsDocShellLoadState* aLoadState,
  mSrcdocData = aLoadState->SrcdocData();
  mBaseURI = aLoadState->BaseURI();
  mOriginalUriString = aLoadState->GetOriginalURIString();
-  if (documentContext &&
-      StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+  if (documentContext && StaticPrefs::fission_sessionHistoryInParent()) {
    // It's hard to know at this point whether session history will be enabled
    // in the browsing context, so we always create an entry for a load here.
    mLoadingSessionHistoryInfo =
--- a/netwerk/ipc/ParentProcessDocumentChannel.cpp
+++ b/netwerk/ipc/ParentProcessDocumentChannel.cpp
@ -69,8 +69,7 @@ ParentProcessDocumentChannel::RedirectToRealChannel(
  mStreamFilterEndpoints = std::move(aStreamFilterEndpoints);

  if (mDocumentLoadListener->IsDocumentLoad() &&
-      StaticPrefs::fission_sessionHistoryInParent_AtStartup() &&
-      GetDocShell()) {
+      StaticPrefs::fission_sessionHistoryInParent() && GetDocShell()) {
    GetDocShell()->SetLoadingSessionHistoryInfo(
        *mDocumentLoadListener->GetLoadingSessionHistoryInfo());
  }
--- a/toolkit/components/sessionstore/SessionStoreListener.cpp
+++ b/toolkit/components/sessionstore/SessionStoreListener.cpp
@ -46,8 +46,7 @@ ContentSessionStore::ContentSessionStore(nsIDocShell* aDocShell)
      mFormDataChanged(NO_CHANGE),
      mStorageStatus(NO_STORAGE),
      mDocCapChanged(false),
-      mSHistoryInParent(
-          StaticPrefs::fission_sessionHistoryInParent_AtStartup()),
+      mSHistoryInParent(StaticPrefs::fission_sessionHistoryInParent()),
      mSHistoryChanged(false),
      mSHistoryChangedFromParent(false) {
  MOZ_ASSERT(mDocShell);
@ -170,8 +169,7 @@ TabListener::TabListener(nsIDocShell* aDocShell, Element* aElement)
      mTimeoutDisabled(false),
      mUpdateInterval(15000),
      mEpoch(0),
-      mSHistoryInParent(
-          StaticPrefs::fission_sessionHistoryInParent_AtStartup()) {
+      mSHistoryInParent(StaticPrefs::fission_sessionHistoryInParent()) {
  MOZ_ASSERT(mDocShell);
 }