diff --git a/pkgs/applications/networking/browsers/firefox/packages/firefox-beta.nix b/pkgs/applications/networking/browsers/firefox/packages/firefox-beta.nix
index 3dd7f5a0cceb..6133d8c87ebf 100644
--- a/pkgs/applications/networking/browsers/firefox/packages/firefox-beta.nix
+++ b/pkgs/applications/networking/browsers/firefox/packages/firefox-beta.nix
@@ -10,11 +10,11 @@
 buildMozillaMach rec {
   pname = "firefox-beta";
   binaryName = pname;
-  version = "140.0b3";
+  version = "140.0b4";
   applicationName = "Firefox Beta";
   src = fetchurl {
     url = "mirror://mozilla/firefox/releases/${version}/source/firefox-${version}.source.tar.xz";
-    sha512 = "282b30284e9efa3909e1c1e8b01fd3c8ce5083668a01dea53487aa00d89734889e033051de3ce9aa66d7a84f4d4ac1c6e558fa4e3efe1e51077fc0831e989129";
+    sha512 = "ec3d3377db8629742d428cceded3c7c92ba952f1b9cb6a15eae7f053213c3a377287a577c33b291a5e4d3cbbf918be52a31c3f4ac5f6d06c1f5edfc6312656fe";
   };
 
   meta = {