diff --git a/dom/base/nsObjectLoadingContent.cpp b/dom/base/nsObjectLoadingContent.cpp
index ae0dc8a0256..21c5b9eeeae 100644
--- a/dom/base/nsObjectLoadingContent.cpp
+++ b/dom/base/nsObjectLoadingContent.cpp
@@ -698,7 +698,6 @@ nsObjectLoadingContent::UpdateObjectParameters() {
 
   nsresult rv;
   nsAutoCString newMime;
-  nsAutoString typeAttr;
   nsCOMPtr<nsIURI> newURI;
   nsCOMPtr<nsIURI> newBaseURI;
   ObjectType newType;
@@ -726,7 +725,6 @@ nsObjectLoadingContent::UpdateObjectParameters() {
       el->HasNonEmptyAttr(nsGkAtoms::classid)) {
     // We don't support class ID plugin references, so we should always treat
     // having class Ids as attributes as invalid, and fallback accordingly.
-    newMime.Truncate();
     stateInvalid = true;
   }
 
@@ -756,16 +754,6 @@ nsObjectLoadingContent::UpdateObjectParameters() {
     newBaseURI = docBaseURI;
   }
 
-  nsAutoString rawTypeAttr;
-  el->GetAttr(nsGkAtoms::type, rawTypeAttr);
-  if (!rawTypeAttr.IsEmpty()) {
-    typeAttr = rawTypeAttr;
-    nsAutoString params;
-    nsAutoString mime;
-    nsContentUtils::SplitMimeType(rawTypeAttr, mime, params);
-    CopyUTF16toUTF8(mime, newMime);
-  }
-
   ///
   /// URI
   ///
@@ -800,6 +788,34 @@ nsObjectLoadingContent::UpdateObjectParameters() {
     }
   }
 
+  ///
+  /// type
+  ///
+  nsAutoString rawTypeAttr;
+  el->GetAttr(nsGkAtoms::type, rawTypeAttr);
+  // YouTube embeds might be using type="application/x-shockwave-flash"
+  // which needs to be allowed, but must not override the text/html MIME set
+  // above.
+  if (!mRewrittenYoutubeEmbed && !rawTypeAttr.IsEmpty()) {
+    nsAutoString params;
+    nsAutoString mime;
+    nsContentUtils::SplitMimeType(rawTypeAttr, mime, params);
+
+    if (!StaticPrefs::dom_object_embed_type_hint_enabled()) {
+      NS_ConvertUTF16toUTF8 mimeUTF8(mime);
+      if (GetTypeOfContent(mimeUTF8) != ObjectType::Document) {
+        LOG(
+            ("OBJLC [%p]: MIME '%s' from type attribute is not supported, "
+             "forcing fallback.",
+             this, mimeUTF8.get()));
+        stateInvalid = true;
+      }
+      // Don't use the type attribute as a Content-Type hint.
+    } else {
+      CopyUTF16toUTF8(mime, newMime);
+    }
+  }
+
   ///
   /// Check if the original (pre-channel) content-type or URI changed, and
   /// record mOriginal{ContentType,URI}
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index b821534f587..abbd0b29636 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -3703,6 +3703,13 @@
   value: false
   mirror: always
 
+# Whether the type attribute in an <object> is used as a hint for the Content-Type
+# of the loading document.
+- name: dom.object_embed.type_hint.enabled
+  type: bool
+  value: false
+  mirror: always
+
 # Whether origin trials are enabled.
 - name: dom.origin-trials.enabled
   type: bool