diff --git a/Casks/firefoxnightly.rb b/Casks/firefoxnightly.rb
index 5a5f8bb88..21ccdb68c 100644
--- a/Casks/firefoxnightly.rb
+++ b/Casks/firefoxnightly.rb
@@ -1,5 +1,5 @@
 cask 'firefoxnightly' do
-  version '53.0a1'
+  version '55.0a1'
   sha256 :no_check # required as upstream package is updated in-place
 
   language 'en', default: true do