--- a/devtools/client/jsonview/test/browser_jsonview_save_json.js
+++ b/devtools/client/jsonview/test/browser_jsonview_save_json.js
@@ -47,17 +47,21 @@ function awaitFileSave(name, ext) {
         resolve(destFile);
       };
     };
   });
 }
 
 function getFileContents(file) {
   return new Promise((resolve, reject) => {
-    NetUtil.asyncFetch(file, function(inputStream, status) {
+    let channel = NetUtil.newChannel({
+      uri: NetUtil.newURI(file),
+      loadUsingSystemPrincipal: true,
+    });
+    NetUtil.asyncFetch(channel, function(inputStream, status) {
       if (Components.isSuccessCode(status)) {
         info("Fetched downloaded contents.");
         resolve(NetUtil.readInputStreamToString(inputStream, inputStream.available()));
       } else {
         reject();
       }
     });
   });

--- a/netwerk/base/NetUtil.jsm
+++ b/netwerk/base/NetUtil.jsm
@@ -229,58 +229,22 @@ var NetUtil = {
      *            These will be used as values for the nsILoadInfo object on the
      *            created channel. For details, see nsILoadInfo in nsILoadInfo.idl
      *          loadUsingSystemPrincipal:
      *            Set this to true to use the system principal as
      *            loadingPrincipal.  This must be omitted if loadingPrincipal or
      *            loadingNode are present.
      *            This should be used with care as it skips security checks.
      *        }
-     * @param aOriginCharset [deprecated]
-     *        The character set for the URI.  Only used if aWhatToLoad is a
-     *        string, which is a deprecated API.  Must be undefined otherwise.
-     *        Use NetUtil.newURI if you need to use this option.
-     * @param aBaseURI [deprecated]
-     *        The base URI for the spec.  Only used if aWhatToLoad is a string,
-     *        which is a deprecated API.  Must be undefined otherwise.  Use
-     *        NetUtil.newURI if you need to use this option.
      * @return an nsIChannel object.
      */
-    newChannel: function NetUtil_newChannel(aWhatToLoad, aOriginCharset, aBaseURI)
+    newChannel: function NetUtil_newChannel(aWhatToLoad)
     {
-        // Check for the deprecated API first.
-        if (typeof aWhatToLoad == "string" ||
-            (aWhatToLoad instanceof Ci.nsIFile) ||
-            (aWhatToLoad instanceof Ci.nsIURI)) {
-
-            let uri = (aWhatToLoad instanceof Ci.nsIURI)
-                      ? aWhatToLoad
-                      : this.newURI(aWhatToLoad, aOriginCharset, aBaseURI);
-
-            // log deprecation warning for developers.
-            Services.console.logStringMessage(
-              "Warning: NetUtil.newChannel(uri) deprecated, please provide argument 'aWhatToLoad'");
-
-            // Provide default loadinfo arguments and call the new API.
-            let systemPrincipal =
-              Services.scriptSecurityManager.getSystemPrincipal();
-
-            return this.ioService.newChannelFromURI2(
-                     uri,
-                     null, // loadingNode
-                     systemPrincipal, // loadingPrincipal
-                     null, // triggeringPrincipal
-                     Ci.nsILoadInfo.SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
-                     Ci.nsIContentPolicy.TYPE_OTHER);
-        }
-
-        // We are using the updated API, that requires only the options object.
-        if (typeof aWhatToLoad != "object" ||
-             aOriginCharset !== undefined ||
-             aBaseURI !== undefined) {
+        // Make sure the API is called using only the options object.
+        if (typeof aWhatToLoad != "object" || arguments.length != 1) {
             throw new Components.Exception(
                 "newChannel requires a single object argument",
                 Cr.NS_ERROR_INVALID_ARG,
                 Components.stack.caller
             );
         }
 
         let { uri,

--- a/netwerk/base/nsIIOService.idl
+++ b/netwerk/base/nsIIOService.idl
@@ -132,38 +132,16 @@ interface nsIIOService : nsISupports
                            in nsIURI aBaseURI,
                            in nsIDOMNode aLoadingNode,
                            in nsIPrincipal aLoadingPrincipal,
                            in nsIPrincipal aTriggeringPrincipal,
                            in unsigned long aSecurityFlags,
                            in unsigned long aContentPolicyType);
 
     /**
-     * ***** DEPRECATED *****
-     * Please use NewChannelFromURI2()
-     *
-     * Creates a channel for a given URI.
-     *
-     * @param aURI nsIURI from which to make a channel
-     * @return reference to the new nsIChannel object
-     */
-    nsIChannel newChannelFromURI(in nsIURI aURI);
-
-    /**
-     * ***** DEPRECATED *****
-     * Please use newChannel2().
-     *
-     * Equivalent to newChannelFromURI(newURI(...))
-     */
-    nsIChannel newChannel(in AUTF8String aSpec,
-                          in string aOriginCharset,
-                          in nsIURI aBaseURI);
-
-
-    /**
      * Returns true if networking is in "offline" mode. When in offline mode, 
      * attempts to access the network will fail (although this does not 
      * necessarily correlate with whether there is actually a network 
      * available -- that's hard to detect without causing the dialer to 
      * come up).
      *
      * Changing this fires observer notifications ... see below.
      */

--- a/netwerk/base/nsIOService.cpp
+++ b/netwerk/base/nsIOService.cpp
@@ -1,15 +1,14 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* vim:set ts=4 sw=4 cindent et: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#include "mozilla/ArrayUtils.h"
 #include "mozilla/DebugOnly.h"
 
 #include "nsIOService.h"
 #include "nsIDOMNode.h"
 #include "nsIProtocolHandler.h"
 #include "nsIFileProtocolHandler.h"
 #include "nscore.h"
 #include "nsIURI.h"
@@ -26,17 +25,16 @@
 #include "nsNetCID.h"
 #include "nsCRT.h"
 #include "nsSecCheckWrapChannel.h"
 #include "nsSimpleNestedURI.h"
 #include "nsTArray.h"
 #include "nsIConsoleService.h"
 #include "nsIUploadChannel2.h"
 #include "nsXULAppAPI.h"
-#include "nsIScriptError.h"
 #include "nsIScriptSecurityManager.h"
 #include "nsIProtocolProxyCallback.h"
 #include "nsICancelable.h"
 #include "nsINetworkLinkService.h"
 #include "nsPISocketTransportService.h"
 #include "nsAsyncRedirectVerifyHelper.h"
 #include "nsURLHelper.h"
 #include "nsIProtocolProxyService2.h"
@@ -755,51 +753,16 @@ nsIOService::NewChannelFromURIWithClient
                                                    aTriggeringPrincipal,
                                                    aLoadingClientInfo,
                                                    aController,
                                                    aSecurityFlags,
                                                    aContentPolicyType,
                                                    aResult);
 }
 
-/*  ***** DEPRECATED *****
- * please use NewChannelFromURI2 providing the right arguments for:
- *        * aLoadingNode
- *        * aLoadingPrincipal
- *        * aTriggeringPrincipal
- *        * aSecurityFlags
- *        * aContentPolicyType
- *
- * See nsIIoService.idl for a detailed description of those arguments
- */
-NS_IMETHODIMP
-nsIOService::NewChannelFromURI(nsIURI *aURI, nsIChannel **result)
-{
-  NS_ASSERTION(false, "Deprecated, use NewChannelFromURI2 providing loadInfo arguments!");
-
-  const char16_t* params[] = {
-    u"nsIOService::NewChannelFromURI()",
-    u"nsIOService::NewChannelFromURI2()"
-  };
-  nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
-                                  NS_LITERAL_CSTRING("Security by Default"),
-                                  nullptr, // aDocument
-                                  nsContentUtils::eNECKO_PROPERTIES,
-                                  "APIDeprecationWarning",
-                                  params, ArrayLength(params));
-
-  return NewChannelFromURI2(aURI,
-                            nullptr, // aLoadingNode
-                            nsContentUtils::GetSystemPrincipal(),
-                            nullptr, // aTriggeringPrincipal
-                            nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
-                            nsIContentPolicy::TYPE_OTHER,
-                            result);
-}
-
 NS_IMETHODIMP
 nsIOService::NewChannelFromURIWithLoadInfo(nsIURI* aURI,
                                            nsILoadInfo* aLoadInfo,
                                            nsIChannel** result)
 {
   return NewChannelFromURIWithProxyFlagsInternal(aURI,
                                                  nullptr, // aProxyURI
                                                  0,       // aProxyFlags
@@ -1011,54 +974,16 @@ nsIOService::NewChannel2(const nsACStrin
                               aLoadingNode,
                               aLoadingPrincipal,
                               aTriggeringPrincipal,
                               aSecurityFlags,
                               aContentPolicyType,
                               result);
 }
 
-/*  ***** DEPRECATED *****
- * please use NewChannel2 providing the right arguments for:
- *        * aLoadingNode
- *        * aLoadingPrincipal
- *        * aTriggeringPrincipal
- *        * aSecurityFlags
- *        * aContentPolicyType
- *
- * See nsIIoService.idl for a detailed description of those arguments
- */
-NS_IMETHODIMP
-nsIOService::NewChannel(const nsACString &aSpec, const char *aCharset, nsIURI *aBaseURI, nsIChannel **result)
-{
-  NS_ASSERTION(false, "Deprecated, use NewChannel2 providing loadInfo arguments!");
-
-  const char16_t* params[] = {
-    u"nsIOService::NewChannel()",
-    u"nsIOService::NewChannel2()"
-  };
-  nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
-                                  NS_LITERAL_CSTRING("Security by Default"),
-                                  nullptr, // aDocument
-                                  nsContentUtils::eNECKO_PROPERTIES,
-                                  "APIDeprecationWarning",
-                                  params, ArrayLength(params));
-
-  // Call NewChannel2 providing default arguments for the loadInfo.
-  return NewChannel2(aSpec,
-                     aCharset,
-                     aBaseURI,
-                     nullptr, // aLoadingNode
-                     nsContentUtils::GetSystemPrincipal(), // aLoadingPrincipal
-                     nullptr, // aTriggeringPrincipal
-                     nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
-                     nsIContentPolicy::TYPE_OTHER,
-                     result);
-}
-
 bool
 nsIOService::IsLinkUp()
 {
     InitializeNetworkLinkService();
 
     if (!mNetworkLinkService) {
         // We cannot decide, assume the link is up
         return true;

--- a/netwerk/locales/en-US/necko.properties
+++ b/netwerk/locales/en-US/necko.properties
@@ -38,15 +38,11 @@ DirFileLabel=File:
 PhishingAuth=You are about to visit “%1$S”. This site may be attempting to trick you into thinking you are visiting a different site. Use extreme caution.
 PhishingAuthAccept=I understand and will be very careful
 SuperfluousAuth=You are about to log in to the site “%1$S” with the username “%2$S”, but the website does not require authentication. This may be an attempt to trick you.\n\nIs “%1$S” the site you want to visit?
 AutomaticAuth=You are about to log in to the site “%1$S” with the username “%2$S”.
 
 TrackingUriBlocked=The resource at “%1$S” was blocked because tracking protection is enabled.
 UnsafeUriBlocked=The resource at “%1$S” was blocked by Safe Browsing.
 
-# LOCALIZATION NOTE (APIDeprecationWarning):
-# %1$S is the deprecated API; %2$S is the API function that should be used.
-APIDeprecationWarning=Warning: ‘%1$S’ deprecated, please use ‘%2$S’
-
 # LOCALIZATION NOTE (nsICookieManagerAPIDeprecated): don't localize originAttributes.
 # %1$S is the deprecated API; %2$S is the interface suffix that the given deprecated API belongs to.
 nsICookieManagerAPIDeprecated=“%1$S” is changed. Update your code and pass the correct originAttributes. Read more on MDN: https://developer.mozilla.org/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsICookieManager%2$S

--- a/netwerk/test/unit/test_NetUtil.js
+++ b/netwerk/test/unit/test_NetUtil.js
@@ -631,76 +631,16 @@ function test_newChannel_with_wrong_opti
       loadingPrincipal: systemPrincipal,
       loadUsingSystemPrincipal: true,
     });
   }, /does not accept 'loadUsingSystemPrincipal'/);
 
   run_next_test();
 }
 
-function test_deprecated_newChannel_API_with_string() {
-  const TEST_SPEC = "http://mozilla.org";
-  let uri = NetUtil.newURI(TEST_SPEC);
-  let oneArgChannel = NetUtil.newChannel(TEST_SPEC);
-  let threeArgChannel = NetUtil.newChannel(TEST_SPEC, null, null);
-  Assert.ok(uri.equals(oneArgChannel.URI));
-  Assert.ok(uri.equals(threeArgChannel.URI));
-
-  run_next_test();
-}
-
-function test_deprecated_newChannel_API_with_nsIFile()
-{
-  const TEST_DATA = "this is a test string";
-
-  // First we need a file to read from.
-  let file = Cc["@mozilla.org/file/directory_service;1"].
-             getService(Ci.nsIProperties).
-             get("ProfD", Ci.nsIFile);
-  file.append("NetUtil-deprecated-newchannel-api-test-file.tmp");
-  file.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o666);
-
-  // Write the test data to the file.
-  let ostream = Cc["@mozilla.org/network/file-output-stream;1"].
-                createInstance(Ci.nsIFileOutputStream);
-  ostream.init(file, -1, -1, 0);
-  ostream.write(TEST_DATA, TEST_DATA.length);
-
-  // Sanity check to make sure the data was written.
-  Assert.equal(TEST_DATA, getFileContents(file));
-
-  // create a channel using the file
-  let channel = NetUtil.newChannel(file);
-
-  // Create a pipe that will create our output stream that we can use once
-  // we have gotten all the data.
-  let pipe = Cc["@mozilla.org/pipe;1"].createInstance(Ci.nsIPipe);
-  pipe.init(true, true, 0, 0, null);
-
-  let listener = Cc["@mozilla.org/network/simple-stream-listener;1"].
-                   createInstance(Ci.nsISimpleStreamListener);
-  listener.init(pipe.outputStream, {
-    onStartRequest: function(aRequest, aContext) {},
-    onStopRequest: function(aRequest, aContext, aStatusCode) {
-      pipe.outputStream.close();
-      Assert.ok(Components.isSuccessCode(aContext));
-
-      // Check that we got the right data.
-      Assert.equal(pipe.inputStream.available(), TEST_DATA.length);
-      let is = Cc["@mozilla.org/scriptableinputstream;1"].
-               createInstance(Ci.nsIScriptableInputStream);
-      is.init(pipe.inputStream);
-      let result = is.read(TEST_DATA.length);
-      Assert.equal(TEST_DATA, result);
-      run_next_test();
-    }
-  });
-  channel.asyncOpen2(listener);
-}
-
 function test_readInputStreamToString()
 {
   const TEST_DATA = "this is a test string\0 with an embedded null";
   let istream = Cc["@mozilla.org/io/string-input-stream;1"].
                 createInstance(Ci.nsISupportsCString);
   istream.data = TEST_DATA;
 
   Assert.equal(NetUtil.readInputStreamToString(istream, TEST_DATA.length),
@@ -847,18 +787,16 @@ function test_readInputStreamToString_in
   test_asyncFetch_with_nsIFile,
   test_asyncFetch_with_nsIInputString,
   test_asyncFetch_does_not_block,
   test_newChannel_no_specifier,
   test_newChannel_with_string,
   test_newChannel_with_nsIURI,
   test_newChannel_with_options,
   test_newChannel_with_wrong_options,
-  test_deprecated_newChannel_API_with_string,
-  test_deprecated_newChannel_API_with_nsIFile,
   test_readInputStreamToString,
   test_readInputStreamToString_no_input_stream,
   test_readInputStreamToString_no_bytes_arg,
   test_readInputStreamToString_blocking_stream,
   test_readInputStreamToString_too_many_bytes,
   test_readInputStreamToString_with_charset,
   test_readInputStreamToString_invalid_sequence,
 ].forEach(f => add_test(f));