--- a/toolkit/modules/addons/WebRequest.jsm
+++ b/toolkit/modules/addons/WebRequest.jsm
@@ -752,18 +752,20 @@ HttpObserverManager = {
         }
 
         if (opts.requestHeaders) {
           requestHeaders = requestHeaders || new RequestHeaderChanger(channel);
           data.requestHeaders = requestHeaders.toArray();
         }
 
         if (opts.responseHeaders) {
-          responseHeaders = responseHeaders || new ResponseHeaderChanger(channel);
-          data.responseHeaders = responseHeaders.toArray();
+          try {
+            responseHeaders = responseHeaders || new ResponseHeaderChanger(channel);
+            data.responseHeaders = responseHeaders.toArray();
+          } catch (e) { /* headers may not be available on some redirects */ }
         }
 
         if (opts.requestBody && channel.canModify) {
           requestBody = requestBody || WebRequestUpload.createRequestBody(channel.channel);
           data.requestBody = requestBody;
         }
 
         try {