Bug 1887839 - Remove fission.remoteObjectEmbed pref r=farre

Differential Revision: https://phabricator.services.mozilla.com/D206574

dom/base/test/test_embed_xorigin_document.html

@@ -12,11 +12,6 @@ const testPath = window.location.href.replace("http://mochi.test:8888", "");
 const testDir = testPath.substring(0, testPath.lastIndexOf('/') + 1);
 
 add_task(async function() {
-  // FIXME: Remove when bug 1658342 is fixed
-  await SpecialPowers.pushPrefEnv({
-    set: [["fission.remoteObjectEmbed", true]],
-  });
-
   info("Loading image in embed");
   let embed = document.createElement("embed");
   document.body.appendChild(embed);

modules/libpref/init/StaticPrefList.yaml

@@ -5123,15 +5123,6 @@
   value: false
   mirror: always
 
-# If true, allow process-switching documents loaded by <object> and <embed>
-# elements into a remote process.
-# NOTE: This pref has no impact outside of windows with the
-# `useRemoteSubframes` flag set.
-- name: fission.remoteObjectEmbed
-  type: bool
-  value: true
-  mirror: always
-
 # The strategy used to control how sites are isolated into separate processes
 # when Fisison is enabled. This pref has no effect if Fission is disabled.
 # See the `WebContentIsolationStrategy` enum in `ProcessIsolation.cpp`.

netwerk/ipc/DocumentLoadListener.cpp

@@ -1997,12 +1997,6 @@ bool DocumentLoadListener::MaybeTriggerProcessSwitch(
     return false;
   }
 
-  if (!StaticPrefs::fission_remoteObjectEmbed()) {
-    MOZ_LOG(gProcessIsolationLog, LogLevel::Verbose,
-            ("Process Switch Abort: remote <object>/<embed> disabled"));
-    return false;
-  }
-
   mObjectUpgradeHandler->UpgradeObjectLoad()->Then(
       GetMainThreadSerialEventTarget(), __func__,
       [self = RefPtr{this}, options, parentWindow](