Backed out 2 changesets (bug 1875040) for causing performance regression - Bug 1877481. CLOSED TREE

Backed out changeset 8af7503ecb57 (bug 1875040)
Backed out changeset 0e77ff8e2bfc (bug 1875040)

Author: Iulian Moraru

docshell/base/nsDocShell.cpp

@@ -9436,7 +9436,7 @@ nsresult nsDocShell::InternalLoad(nsDocShellLoadState* aLoadState,
   // separate check for SHIP so that we know if there are ongoing requests
   // before calling Stop() below.
   if (mozilla::SessionHistoryInParent()) {
-    Document* document = GetExtantDocument();
+    Document* document = GetDocument();
     uint32_t flags = 0;
     if (document && !document->CanSavePresentation(nullptr, flags, true)) {
       // This forces some flags into the WindowGlobalParent's mBFCacheStatus,

remote/cdp/observers/ContextObserver.sys.mjs

@@ -34,6 +34,8 @@ export class ContextObserver {
     this.chromeEventHandler = chromeEventHandler;
     lazy.EventEmitter.decorate(this);
 
+    this._fissionEnabled = Services.appinfo.fissionAutostart;
+
     this.chromeEventHandler.addEventListener("DOMWindowCreated", this, {
       mozSystemGroup: true,
     });
@@ -49,7 +51,11 @@ export class ContextObserver {
     Services.obs.addObserver(this, "document-element-inserted");
     Services.obs.addObserver(this, "inner-window-destroyed");
 
-    Services.obs.addObserver(this, "webnavigation-create");
+    // With Fission disabled the `DOMWindowCreated` event is fired too late.
+    // Use the `webnavigation-create` notification instead.
+    if (!this._fissionEnabled) {
+      Services.obs.addObserver(this, "webnavigation-create");
+    }
     Services.obs.addObserver(this, "webnavigation-destroy");
   }
 
@@ -67,7 +73,9 @@ export class ContextObserver {
     Services.obs.removeObserver(this, "document-element-inserted");
     Services.obs.removeObserver(this, "inner-window-destroyed");
 
-    Services.obs.removeObserver(this, "webnavigation-create");
+    if (!this._fissionEnabled) {
+      Services.obs.removeObserver(this, "webnavigation-create");
+    }
     Services.obs.removeObserver(this, "webnavigation-destroy");
   }
 
@@ -83,6 +91,13 @@ export class ContextObserver {
         // what ExecutionContext(s) to destroy.
         this.emit("context-destroyed", { frameId });
 
+        // With Fission enabled the frame is attached early enough so that
+        // expected network requests and responses are handles afterward.
+        // Otherwise send the event when `webnavigation-create` is received.
+        if (this._fissionEnabled) {
+          this.emit("frame-attached", { frameId, window });
+        }
+
         break;
 
       case "pageshow":