diff --git a/Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp b/Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp
index 39fb3c865b0..84ccc211eda 100644
--- a/Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp
+++ b/Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp
@@ -45,6 +45,7 @@ static bool url_matches_about_blank(AK::URL const& url)
         && url.host().is_null();
 }
 
+// FIXME: This is an outdated older version of "determining the origin" and should be removed.
 // https://html.spec.whatwg.org/multipage/browsers.html#determining-the-origin
 HTML::Origin determine_the_origin(BrowsingContext const& browsing_context, Optional<AK::URL> url, SandboxingFlagSet sandbox_flags, Optional<HTML::Origin> invocation_origin)
 {
@@ -73,6 +74,34 @@ HTML::Origin determine_the_origin(BrowsingContext const& browsing_context, Optio
     return URL::url_origin(*url);
 }
 
+// https://html.spec.whatwg.org/multipage/document-sequences.html#determining-the-origin
+HTML::Origin determine_the_origin(AK::URL const& url, SandboxingFlagSet sandbox_flags, Optional<HTML::Origin> source_origin, Optional<HTML::Origin> container_origin)
+{
+    // 1. If sandboxFlags has its sandboxed origin browsing context flag set, then return a new opaque origin.
+    if (sandbox_flags.flags & SandboxingFlagSet::SandboxedOrigin) {
+        return HTML::Origin {};
+    }
+
+    // FIXME: 2. If url is null, then return a new opaque origin.
+    // FIXME: There appears to be no way to get a null URL here, so it might be a spec bug.
+
+    // 3. If url is about:srcdoc, then:
+    if (url == "about:srcdoc"sv) {
+        // 1. Assert: containerOrigin is non-null.
+        VERIFY(container_origin.has_value());
+
+        // 2. Return containerOrigin.
+        return container_origin.release_value();
+    }
+
+    // 4. If url matches about:blank and sourceOrigin is non-null, then return sourceOrigin.
+    if (url_matches_about_blank(url) && source_origin.has_value())
+        return source_origin.release_value();
+
+    // 5. Return url's origin.
+    return URL::url_origin(url);
+}
+
 // https://html.spec.whatwg.org/multipage/browsers.html#creating-a-new-top-level-browsing-context
 JS::NonnullGCPtr<BrowsingContext> BrowsingContext::create_a_new_top_level_browsing_context(Web::Page& page)
 {
diff --git a/Userland/Libraries/LibWeb/HTML/BrowsingContext.h b/Userland/Libraries/LibWeb/HTML/BrowsingContext.h
index 6e70d92187d..833039a3000 100644
--- a/Userland/Libraries/LibWeb/HTML/BrowsingContext.h
+++ b/Userland/Libraries/LibWeb/HTML/BrowsingContext.h
@@ -330,6 +330,9 @@ private:
     bool m_has_been_discarded { false };
 };
 
+// FIXME: Remove this once everything is switched to the new overload.
 HTML::Origin determine_the_origin(BrowsingContext const& browsing_context, Optional<AK::URL> url, SandboxingFlagSet sandbox_flags, Optional<HTML::Origin> invocation_origin);
 
+HTML::Origin determine_the_origin(AK::URL const& url, SandboxingFlagSet sandbox_flags, Optional<HTML::Origin> source_origin, Optional<HTML::Origin> container_origin);
+
 }