diff --git a/dom/xhr/XMLHttpRequestMainThread.cpp b/dom/xhr/XMLHttpRequestMainThread.cpp
index c9a7391b1bc7..7bd4a247294b 100644
--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -2500,27 +2500,6 @@ XMLHttpRequestMainThread::CreateChannel()
     secFlags |= nsILoadInfo::SEC_COOKIES_OMIT;
   }
 
-  nsCOMPtr<nsIExpandedPrincipal> ep = do_QueryInterface(mPrincipal);
-  if (ep) {
-    // If we have an expanded principal, instead of using that, select the
-    // principal in the whitelist which can load our URL, and use that instead.
-    nsTArray<nsCOMPtr<nsIPrincipal>>* whitelist = nullptr;
-    ep->GetWhiteList(&whitelist);
-    if (!whitelist) {
-      return NS_ERROR_FAILURE;
-    }
-    MOZ_ASSERT(!(secFlags & nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_DATA_INHERITS));
-    bool dataInherits = (secFlags &
-      (nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_INHERITS |
-       nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS)) != 0;
-    for (const auto& principal : *whitelist) {
-      if (NS_SUCCEEDED(principal->CheckMayLoad(mRequestURL, false, dataInherits))) {
-        mPrincipal = principal;
-        break;
-      }
-    }
-  }
-
   // Use the responsibleDocument if we have it, except for dedicated workers
   // where it will be the parent document, which is not the one we want to use.
   nsresult rv;
@@ -2559,6 +2538,35 @@ XMLHttpRequestMainThread::CreateChannel()
     }
   }
 
+  // Using the provided principal as the triggeringPrincipal is fine, since we
+  // want to be able to access any of the origins that the principal has access
+  // to during the security checks, but we don't want a document to inherit an
+  // expanded principal, so in that case we need to select the principal in the
+  // expanded principal's whitelist that can load our URL as principalToInherit.
+  nsCOMPtr<nsIPrincipal> resultingDocumentPrincipal(mPrincipal);
+  nsCOMPtr<nsIExpandedPrincipal> ep = do_QueryInterface(mPrincipal);
+  if (ep) {
+    nsTArray<nsCOMPtr<nsIPrincipal>>* whitelist = nullptr;
+    ep->GetWhiteList(&whitelist);
+    if (!whitelist) {
+      return NS_ERROR_FAILURE;
+    }
+    MOZ_ASSERT(!(secFlags & nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_DATA_INHERITS));
+    bool dataInherits = (secFlags &
+      (nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_INHERITS |
+       nsILoadInfo::SEC_REQUIRE_CORS_DATA_INHERITS)) != 0;
+    for (const auto& principal : *whitelist) {
+      if (NS_SUCCEEDED(principal->CheckMayLoad(mRequestURL, false, dataInherits))) {
+        resultingDocumentPrincipal = principal;
+        break;
+      }
+    }
+  }
+
+  nsCOMPtr<nsILoadInfo> loadInfo = mChannel->GetLoadInfo();
+  rv = loadInfo->SetPrincipalToInherit(resultingDocumentPrincipal);
+  NS_ENSURE_SUCCESS(rv, rv);
+
   return NS_OK;
 }
 
diff --git a/js/xpconnect/tests/unit/test_allowedDomainsXHR.js b/js/xpconnect/tests/unit/test_allowedDomainsXHR.js
index fd7c17c34de3..71bfe942ba02 100644
--- a/js/xpconnect/tests/unit/test_allowedDomainsXHR.js
+++ b/js/xpconnect/tests/unit/test_allowedDomainsXHR.js
@@ -4,12 +4,16 @@ cu.import("resource://testing-common/httpd.js");
 
 var httpserver = new HttpServer();
 var httpserver2 = new HttpServer();
+var httpserver3 = new HttpServer();
 var testpath = "/simple";
+var redirectpath = "/redirect";
 var negativetestpath = "/negative";
 var httpbody = "<?xml version='1.0' ?><root>0123456789</root>";
 
 var sb = cu.Sandbox(["http://www.example.com",
-                     "http://localhost:4444/simple"],
+                     "http://localhost:4444/redirect",
+                     "http://localhost:4444/simple",
+                     "http://localhost:4446/redirect"],
                      { wantGlobalProperties: ["XMLHttpRequest"] });
 
 function createXHR(loc, async)
@@ -35,7 +39,7 @@ function checkResults(xhr)
 var httpServersClosed = 0;
 function finishIfDone()
 {
-  if (++httpServersClosed == 2)
+  if (++httpServersClosed == 3)
     do_test_finished();
 }
 
@@ -44,11 +48,15 @@ function run_test()
   do_test_pending();
 
   httpserver.registerPathHandler(testpath, serverHandler);
+  httpserver.registerPathHandler(redirectpath, redirectHandler1);
   httpserver.start(4444);
 
   httpserver2.registerPathHandler(negativetestpath, serverHandler);
   httpserver2.start(4445);
 
+  httpserver3.registerPathHandler(redirectpath, redirectHandler2);
+  httpserver3.start(4446);
+
   // Test sync XHR sending
   cu.evalInSandbox('var createXHR = ' + createXHR.toString(), sb);
   var res = cu.evalInSandbox('var sync = createXHR("4444/simple"); sync.send(null); sync', sb);
@@ -68,7 +76,21 @@ function run_test()
     do_check_true(true);
   }
 
+  // Test redirect handling.
+  // This request bounces to server 2 and then back to server 1.  Neither of
+  // these servers support CORS, but if the expanded principal is used as the
+  // triggering principal, this should work.
+  cu.evalInSandbox('var createXHR = ' + createXHR.toString(), sb);
+  var res = cu.evalInSandbox('var sync = createXHR("4444/redirect"); sync.send(null); sync', sb);
+  do_check_true(checkResults(res));
+
+  var principal = res.responseXML.nodePrincipal;
+  do_check_true(principal.isCodebasePrincipal);
+  var requestURL = "http://localhost:4444/simple";
+  do_check_eq(principal.URI.spec, requestURL);
+
   httpserver2.stop(finishIfDone);
+  httpserver3.stop(finishIfDone);
 
   // Test async XHR sending
   sb.finish = function(){
@@ -95,8 +117,20 @@ function run_test()
   async.send(null);
 }
 
-function serverHandler(metadata, response)
+function serverHandler(request, response)
 {
   response.setHeader("Content-Type", "text/xml", false);
   response.bodyOutputStream.write(httpbody, httpbody.length);
 }
+
+function redirectHandler1(request, response)
+{
+  response.setStatusLine(request.httpVersion, 302, "Found");
+  response.setHeader("Location", "http://localhost:4446/redirect", false);
+}
+
+function redirectHandler2(request, response)
+{
+  response.setStatusLine(request.httpVersion, 302, "Found");
+  response.setHeader("Location", "http://localhost:4444/simple", false);
+}