Copied from upstream:
https://hg.mozilla.org/releases/mozilla-esr38/raw-rev/b4467681abd6

# HG changeset patch
# User Gijs Kruitbosch <gijskruitbosch@gmail.com>
# Date 1455276061 0
# Node ID b4467681abd676cd5575cbdf922927f8f54d2ad9
# Parent  8c1d40e45a72c6432e879137a0afa519dc6c9841
Bug 1245264 - r=bz, r=ritu

MozReview-Commit-ID: I0sVdritpD3

diff --git a/dom/base/nsLocation.cpp b/dom/base/nsLocation.cpp
--- a/dom/base/nsLocation.cpp
+++ b/dom/base/nsLocation.cpp
@@ -735,16 +735,27 @@ nsLocation::SetProtocol(const nsAString&
     return rv;
   }
 
   rv = uri->SetScheme(NS_ConvertUTF16toUTF8(aProtocol));
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
   }
 
+  nsAutoCString newSpec;
+  rv = uri->GetSpec(newSpec);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  // We may want a new URI class for the new URI, so recreate it:
+  rv = NS_NewURI(getter_AddRefs(uri), newSpec);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
   return SetURI(uri);
 }
 
 void
 nsLocation::GetUsername(nsAString& aUsername, ErrorResult& aError)
 {
   if (!CallerSubsumes()) {
     aError.Throw(NS_ERROR_DOM_SECURITY_ERR);