diff --git a/RAILS_VERSION b/RAILS_VERSION
index 21cfcbd0d8..6b829f5d9b 100644
--- a/RAILS_VERSION
+++ b/RAILS_VERSION
@@ -1 +1 @@
-6.0.0.beta2
+6.0.0.beta3
diff --git a/actioncable/CHANGELOG.md b/actioncable/CHANGELOG.md
index aa72cec9cb..9f312f8806 100644
--- a/actioncable/CHANGELOG.md
+++ b/actioncable/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   PostgreSQL subscription adapters now support `channel_prefix` option in cable.yml
diff --git a/actioncable/lib/action_cable/gem_version.rb b/actioncable/lib/action_cable/gem_version.rb
index 728b3e90cb..2be81736c6 100644
--- a/actioncable/lib/action_cable/gem_version.rb
+++ b/actioncable/lib/action_cable/gem_version.rb
@@ -10,7 +10,7 @@ module ActionCable
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/actioncable/package.json b/actioncable/package.json
index f6691e10d1..4451afd17f 100644
--- a/actioncable/package.json
+++ b/actioncable/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rails/actioncable",
-  "version": "6.0.0-beta2",
+  "version": "6.0.0-beta3",
   "description": "WebSocket framework for Ruby on Rails.",
   "main": "app/assets/javascripts/action_cable.js",
   "files": [
diff --git a/actionmailbox/CHANGELOG.md b/actionmailbox/CHANGELOG.md
index d47f72fff7..f59c052d63 100644
--- a/actionmailbox/CHANGELOG.md
+++ b/actionmailbox/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   Allow skipping incineration of processed emails.
diff --git a/actionmailbox/lib/action_mailbox/gem_version.rb b/actionmailbox/lib/action_mailbox/gem_version.rb
index e7e3317f16..a063553471 100644
--- a/actionmailbox/lib/action_mailbox/gem_version.rb
+++ b/actionmailbox/lib/action_mailbox/gem_version.rb
@@ -10,7 +10,7 @@ module ActionMailbox
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/actionmailer/CHANGELOG.md b/actionmailer/CHANGELOG.md
index e9d8d07c79..182c43551d 100644
--- a/actionmailer/CHANGELOG.md
+++ b/actionmailer/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   No changes.
diff --git a/actionmailer/lib/action_mailer/gem_version.rb b/actionmailer/lib/action_mailer/gem_version.rb
index 3002fd2ad6..4efcd966db 100644
--- a/actionmailer/lib/action_mailer/gem_version.rb
+++ b/actionmailer/lib/action_mailer/gem_version.rb
@@ -10,7 +10,7 @@ module ActionMailer
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 8eaaee5100..2df6f5fc09 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   Make debug exceptions works in an environment where ActiveStorage is not loaded.
diff --git a/actionpack/lib/action_dispatch/http/mime_negotiation.rb b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
index 498b1e6695..4e81ba12a5 100644
--- a/actionpack/lib/action_dispatch/http/mime_negotiation.rb
+++ b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
@@ -79,6 +79,11 @@ module ActionDispatch
           else
             [Mime[:html]]
           end
+
+          v = v.select do |format|
+            format.symbol || format.ref == "*/*"
+          end
+
           set_header k, v
         end
       end
diff --git a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
index 02ccfbc81a..7c43c781c7 100644
--- a/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
+++ b/actionpack/lib/action_dispatch/middleware/session/cookie_store.rb
@@ -24,9 +24,10 @@ module ActionDispatch
     #
     #   Rails.application.config.session_store :cookie_store, key: '_your_app_session'
     #
-    # By default, your secret key base is derived from your application name in
-    # the test and development environments. In all other environments, it is stored
-    # encrypted in the <tt>config/credentials.yml.enc</tt> file.
+    # In the development and test environments your application's secret key base is
+    # generated by Rails and stored in a temporary file in <tt>tmp/development_secret.txt</tt>.
+    # In all other environments, it is stored encrypted in the
+    # <tt>config/credentials.yml.enc</tt> file.
     #
     # If your application was not updated to Rails 5.2 defaults, the secret_key_base
     # will be found in the old <tt>config/secrets.yml</tt> file.
diff --git a/actionpack/lib/action_pack/gem_version.rb b/actionpack/lib/action_pack/gem_version.rb
index 8007cfe35b..3bbb1734d9 100644
--- a/actionpack/lib/action_pack/gem_version.rb
+++ b/actionpack/lib/action_pack/gem_version.rb
@@ -10,7 +10,7 @@ module ActionPack
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/actionpack/test/controller/mime/respond_to_test.rb b/actionpack/test/controller/mime/respond_to_test.rb
index 00e1d5f3b3..21de05b323 100644
--- a/actionpack/test/controller/mime/respond_to_test.rb
+++ b/actionpack/test/controller/mime/respond_to_test.rb
@@ -125,7 +125,7 @@ class RespondToController < ActionController::Base
   def custom_type_handling
     respond_to do |type|
       type.html { render body: "HTML"    }
-      type.custom("application/crazy-xml")  { render body: "Crazy XML"  }
+      type.custom("application/fancy-xml")  { render body: "Fancy XML"  }
       type.all  { render body: "Nothing" }
     end
   end
@@ -314,12 +314,14 @@ class RespondToControllerTest < ActionController::TestCase
     @request.host = "www.example.com"
     Mime::Type.register_alias("text/html", :iphone)
     Mime::Type.register("text/x-mobile", :mobile)
+    Mime::Type.register("application/fancy-xml", :fancy_xml)
   end
 
   def teardown
     super
     Mime::Type.unregister(:iphone)
     Mime::Type.unregister(:mobile)
+    Mime::Type.unregister(:fancy_xml)
   end
 
   def test_html
@@ -489,10 +491,10 @@ class RespondToControllerTest < ActionController::TestCase
   end
 
   def test_custom_types
-    @request.accept = "application/crazy-xml"
+    @request.accept = "application/fancy-xml"
     get :custom_type_handling
-    assert_equal "application/crazy-xml", @response.content_type
-    assert_equal "Crazy XML", @response.body
+    assert_equal "application/fancy-xml", @response.content_type
+    assert_equal "Fancy XML", @response.body
 
     @request.accept = "text/html"
     get :custom_type_handling
diff --git a/actionpack/test/controller/new_base/content_negotiation_test.rb b/actionpack/test/controller/new_base/content_negotiation_test.rb
index 7205e90176..6de91c57b7 100644
--- a/actionpack/test/controller/new_base/content_negotiation_test.rb
+++ b/actionpack/test/controller/new_base/content_negotiation_test.rb
@@ -20,9 +20,19 @@ module ContentNegotiation
       assert_body "Hello world */*!"
     end
 
-    test "Not all mimes are converted to symbol" do
+    test "A js or */* Accept header will return HTML" do
+      get "/content_negotiation/basic/hello", headers: { "HTTP_ACCEPT" => "text/javascript, */*" }
+      assert_body "Hello world text/html!"
+    end
+
+    test "A js or */* Accept header on xhr will return HTML" do
+      get "/content_negotiation/basic/hello", headers: { "HTTP_ACCEPT" => "text/javascript, */*" }, xhr: true
+      assert_body "Hello world text/javascript!"
+    end
+
+    test "Unregistered mimes are ignored" do
       get "/content_negotiation/basic/all", headers: { "HTTP_ACCEPT" => "text/plain, mime/another" }
-      assert_body '[:text, "mime/another"]'
+      assert_body '[:text]'
     end
   end
 end
diff --git a/actiontext/CHANGELOG.md b/actiontext/CHANGELOG.md
index 203800da1f..b79ff612fb 100644
--- a/actiontext/CHANGELOG.md
+++ b/actiontext/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   No changes.
diff --git a/actiontext/lib/action_text/gem_version.rb b/actiontext/lib/action_text/gem_version.rb
index da2a9212d3..ecd32d5f69 100644
--- a/actiontext/lib/action_text/gem_version.rb
+++ b/actiontext/lib/action_text/gem_version.rb
@@ -10,7 +10,7 @@ module ActionText
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/actiontext/package.json b/actiontext/package.json
index 6408d38765..f67fea1642 100644
--- a/actiontext/package.json
+++ b/actiontext/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rails/actiontext",
-  "version": "6.0.0-beta2",
+  "version": "6.0.0-beta3",
   "description": "Edit and display rich text in Rails applications",
   "main": "app/javascript/actiontext/index.js",
   "files": [
diff --git a/actionview/CHANGELOG.md b/actionview/CHANGELOG.md
index 2e6c37de58..d07794ddf3 100644
--- a/actionview/CHANGELOG.md
+++ b/actionview/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   ActionView::Template.finalize_compiled_template_methods is deprecated with
diff --git a/actionview/lib/action_view/gem_version.rb b/actionview/lib/action_view/gem_version.rb
index c799967cc5..5bed37583e 100644
--- a/actionview/lib/action_view/gem_version.rb
+++ b/actionview/lib/action_view/gem_version.rb
@@ -10,7 +10,7 @@ module ActionView
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/actionview/package.json b/actionview/package.json
index 98827efd62..e5c8b9bb7d 100644
--- a/actionview/package.json
+++ b/actionview/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rails/ujs",
-  "version": "6.0.0-beta2",
+  "version": "6.0.0-beta3",
   "description": "Ruby on Rails unobtrusive scripting adapter",
   "main": "lib/assets/compiled/rails-ujs.js",
   "files": [
diff --git a/activejob/CHANGELOG.md b/activejob/CHANGELOG.md
index f782b2d69f..de375baa9c 100644
--- a/activejob/CHANGELOG.md
+++ b/activejob/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   No changes.
diff --git a/activejob/lib/active_job/gem_version.rb b/activejob/lib/active_job/gem_version.rb
index f303dcddf5..5313a4ab9e 100644
--- a/activejob/lib/active_job/gem_version.rb
+++ b/activejob/lib/active_job/gem_version.rb
@@ -10,7 +10,7 @@ module ActiveJob
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index 71e56e2522..56fbfacbd7 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,26 +1,32 @@
 *   Change how validation error translation strings are fetched: The new behavior
     will first try the more specific keys, including doing locale fallback, then try
     the less specific ones.
-    
+
     For example, this is the order in which keys will now be tried for a `blank`
     error on a `product`'s `title` attribute with current locale set to `en-US`:
- 
+
         en-US.activerecord.errors.models.product.attributes.title.blank
         en-US.activerecord.errors.models.product.blank
         en-US.activerecord.errors.messages.blank
-        
+
         en.activerecord.errors.models.product.attributes.title.blank
         en.activerecord.errors.models.product.blank
         en.activerecord.errors.messages.blank
-        
+
         en-US.errors.attributes.title.blank
         en-US.errors.messages.blank
-        
+
         en.errors.attributes.title.blank
         en.errors.messages.blank
- 
+
     *Hugo Vacher*
 
+
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   Fix date value when casting a multiparameter date hash to not convert
diff --git a/activemodel/lib/active_model/gem_version.rb b/activemodel/lib/active_model/gem_version.rb
index 399e724cea..1626aac468 100644
--- a/activemodel/lib/active_model/gem_version.rb
+++ b/activemodel/lib/active_model/gem_version.rb
@@ -10,7 +10,7 @@ module ActiveModel
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 2d260f2bf5..3d7508252a 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -70,6 +70,11 @@
     *Juani Villarejo*
 
 
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   Fix prepared statements caching to be enabled even when query caching is enabled.
diff --git a/activerecord/lib/active_record/gem_version.rb b/activerecord/lib/active_record/gem_version.rb
index 345441eea8..f77bc2e3c1 100644
--- a/activerecord/lib/active_record/gem_version.rb
+++ b/activerecord/lib/active_record/gem_version.rb
@@ -10,7 +10,7 @@ module ActiveRecord
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/activestorage/CHANGELOG.md b/activestorage/CHANGELOG.md
index ba9204249d..54fc949172 100644
--- a/activestorage/CHANGELOG.md
+++ b/activestorage/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   No changes.
diff --git a/activestorage/lib/active_storage/gem_version.rb b/activestorage/lib/active_storage/gem_version.rb
index 046534fc07..d8f8577cc3 100644
--- a/activestorage/lib/active_storage/gem_version.rb
+++ b/activestorage/lib/active_storage/gem_version.rb
@@ -10,7 +10,7 @@ module ActiveStorage
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/activestorage/package.json b/activestorage/package.json
index 49b9163bd9..c363acebde 100644
--- a/activestorage/package.json
+++ b/activestorage/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rails/activestorage",
-  "version": "6.0.0-beta2",
+  "version": "6.0.0-beta3",
   "description": "Attach cloud and local files in Rails applications",
   "main": "app/assets/javascripts/activestorage.js",
   "files": [
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 219ea8787e..2610cc63a4 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -27,6 +27,11 @@
     *DHH*
 
 
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   New autoloading based on [Zeitwerk](https://github.com/fxn/zeitwerk).
diff --git a/activesupport/lib/active_support/gem_version.rb b/activesupport/lib/active_support/gem_version.rb
index 009bb895a6..cf17922d7d 100644
--- a/activesupport/lib/active_support/gem_version.rb
+++ b/activesupport/lib/active_support/gem_version.rb
@@ -10,7 +10,7 @@ module ActiveSupport
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/guides/CHANGELOG.md b/guides/CHANGELOG.md
index 41037146a0..beace1ed6f 100644
--- a/guides/CHANGELOG.md
+++ b/guides/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   No changes.
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index d2377b3b6d..8163b282aa 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Rails 6.0.0.beta3 (March 11, 2019) ##
+
+*   No changes.
+
+
 ## Rails 6.0.0.beta2 (February 25, 2019) ##
 
 *   Fix non-symbol access to nested hashes returned from `Rails::Application.config_for`
diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index fbad3e5db3..558a4d1f57 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -415,8 +415,8 @@ module Rails
     # then credentials.secret_key_base, and finally secrets.secret_key_base. For most applications,
     # the correct place to store it is in the encrypted credentials file.
     def secret_key_base
-      if Rails.env.test? || Rails.env.development?
-        secrets.secret_key_base || Digest::MD5.hexdigest(self.class.name)
+      if Rails.env.development? || Rails.env.test?
+        secrets.secret_key_base ||= generate_development_secret
       else
         validate_secret_key_base(
           ENV["SECRET_KEY_BASE"] || credentials.secret_key_base || secrets.secret_key_base
@@ -581,6 +581,21 @@ module Rails
 
     private
 
+      def generate_development_secret
+        if secrets.secret_key_base.nil?
+          key_file = Rails.root.join("tmp/development_secret.txt")
+
+          if !File.exist?(key_file)
+            random_key = SecureRandom.hex(64)
+            File.binwrite(key_file, random_key)
+          end
+
+          secrets.secret_key_base = File.binread(key_file)
+        end
+
+        secrets.secret_key_base
+      end
+
       def build_request(env)
         req = super
         env["ORIGINAL_FULLPATH"] = req.fullpath
diff --git a/railties/lib/rails/gem_version.rb b/railties/lib/rails/gem_version.rb
index 249894f9d0..fea24810f5 100644
--- a/railties/lib/rails/gem_version.rb
+++ b/railties/lib/rails/gem_version.rb
@@ -10,7 +10,7 @@ module Rails
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 9ba5517afd..eee2d633be 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -596,6 +596,27 @@ module ApplicationTests
       assert_equal "some_value", verifier.verify(message)
     end
 
+    test "application will generate secret_key_base in tmp file if blank in development" do
+      app_file "config/initializers/secret_token.rb", <<-RUBY
+        Rails.application.credentials.secret_key_base = nil
+      RUBY
+
+      app "development"
+
+      assert_not_nil app.secrets.secret_key_base
+      assert File.exist?(app_path("tmp/development_secret.txt"))
+    end
+
+    test "application will not generate secret_key_base in tmp file if blank in production" do
+      app_file "config/initializers/secret_token.rb", <<-RUBY
+        Rails.application.credentials.secret_key_base = nil
+      RUBY
+
+      assert_raises ArgumentError do
+        app "production"
+      end
+    end
+
     test "raises when secret_key_base is blank" do
       app_file "config/initializers/secret_token.rb", <<-RUBY
         Rails.application.credentials.secret_key_base = nil
@@ -619,7 +640,6 @@ module ApplicationTests
 
     test "application verifier can build different verifiers" do
       make_basic_app do |application|
-        application.credentials.secret_key_base = "b3c631c314c0bbca50c1b2843150fe33"
         application.config.session_store :disabled
       end
 
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index b0662e0159..14cdf1ab7c 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -226,6 +226,7 @@ module TestHelpers
       @app.config.session_store :cookie_store, key: "_myapp_session"
       @app.config.active_support.deprecation = :log
       @app.config.log_level = :info
+      @app.secrets.secret_key_base = "b3c631c314c0bbca50c1b2843150fe33"
 
       yield @app if block_given?
       @app.initialize!
diff --git a/version.rb b/version.rb
index 249894f9d0..fea24810f5 100644
--- a/version.rb
+++ b/version.rb
@@ -10,7 +10,7 @@ module Rails
     MAJOR = 6
     MINOR = 0
     TINY  = 0
-    PRE   = "beta2"
+    PRE   = "beta3"
 
     STRING = [MAJOR, MINOR, TINY, PRE].compact.join(".")
   end