diff --git a/.eslintrc.js b/.eslintrc.js
index f1ab25172b85..091dabb3c6cc 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -87,9 +87,6 @@ module.exports = {
   }, {
     // TODO: Bug 1246594. Empty this list once the rule has landed for all dirs
     "files": [
-      "netwerk/protocol/http/WellKnownOpportunisticUtils.jsm",
-      "netwerk/test/httpserver/httpd.js",
-      "netwerk/test/httpserver/test/**",
       "parser/htmlparser/tests/mochitest/parser_datreader.js",
       "testing/marionette/event.js",
       "testing/mochitest/**",
diff --git a/netwerk/test/httpserver/test/head_utils.js b/netwerk/test/httpserver/test/head_utils.js
index 4b207ac045f0..8f8db44dc04e 100644
--- a/netwerk/test/httpserver/test/head_utils.js
+++ b/netwerk/test/httpserver/test/head_utils.js
@@ -98,25 +98,25 @@ function* LineIterator(data) {
  *   an Iterator which returns lines of text
  * @param expectedLines : [string]
  *   an array of the expected lines of text
- * @throws string
- *   an error message if iter doesn't agree with expectedLines
+ * @throws an error message if iter doesn't agree with expectedLines
  */
 function expectLines(iter, expectedLines) {
   var index = 0;
   for (var line of iter) {
     if (expectedLines.length == index)
-      throw "Error: got more than " + expectedLines.length + " expected lines!";
+      throw new Error(`Error: got more than ${expectedLines.length} expected lines!`);
 
     var expected = expectedLines[index++];
     if (expected !== line)
-      throw "Error on line " + index + "!\n" +
-            "  actual: '" + line + "',\n" +
-            "  expect: '" + expected + "'";
+      throw new Error(`Error on line ${index}!
+  actual: '${line}',
+  expect: '${expected}'`);
   }
 
   if (expectedLines.length !== index) {
-    throw "Expected more lines!  Got " + index +
-          ", expected " + expectedLines.length;
+    throw new Error(
+      `Expected more lines!  Got ${index}, expected ${expectedLines.length}`
+    );
   }
 }
 
diff --git a/netwerk/test/httpserver/test/test_headers.js b/netwerk/test/httpserver/test/test_headers.js
index 45bfa57ce1b4..e9f350754147 100644
--- a/netwerk/test/httpserver/test/test_headers.js
+++ b/netwerk/test/httpserver/test/test_headers.js
@@ -40,8 +40,7 @@ function assertValidHeader(fieldName, fieldValue, headers) {
 function assertInvalidHeader(fieldName, fieldValue, headers) {
   try {
     headers.setHeader(fieldName, fieldValue, false);
-    throw "Setting (" + fieldName + ", " +
-          fieldValue + ") as header succeeded!";
+    throw new Error(`Setting (${fieldName}, ${fieldValue}) as header succeeded!`);
   } catch (e) {
     if (e.result !== Cr.NS_ERROR_INVALID_ARG)
       do_throw("Unexpected exception thrown: " + e);