diff --git a/Casks/firefox-beta.rb b/Casks/firefox-beta.rb
index 8c32acc3a..006578db8 100644
--- a/Casks/firefox-beta.rb
+++ b/Casks/firefox-beta.rb
@@ -1,6 +1,6 @@
 cask :v1 => 'firefox-beta' do
-  version '38.0.5b2'
-  sha256 '51054175be49e60f1210ab76cd9cd46116d9c272efc3181c660f277f8a727216'
+  version '39.0b5'
+  sha256 'a57af5e2a3daf5d9fd51ff51378ac1731fa0e86ff9638a6c539aa7dfd3c16a1a'
 
   url "https://download.mozilla.org/?product=firefox-#{version}-SSL&os=osx&lang=en-US"
   homepage 'https://www.mozilla.org/en-US/firefox/channel/#beta'