diff --git a/pkgs/applications/networking/browsers/firefox/packages.nix b/pkgs/applications/networking/browsers/firefox/packages.nix
index f43eaab9fa00..440d2ea117a1 100644
--- a/pkgs/applications/networking/browsers/firefox/packages.nix
+++ b/pkgs/applications/networking/browsers/firefox/packages.nix
@@ -33,11 +33,11 @@
 
   firefox-beta = buildMozillaMach rec {
     pname = "firefox-beta";
-    version = "121.0b5";
+    version = "121.0b9";
     applicationName = "Mozilla Firefox Beta";
     src = fetchurl {
       url = "mirror://mozilla/firefox/releases/${version}/source/firefox-${version}.source.tar.xz";
-      sha512 = "1c9d2e8fe32687e95af5cf335ef219e70847977568ca636a322c2804f6408d054236df4196e03fc666ac3245ca4a3a9785caf56e1d928a1850f4b34ab5237f8c";
+      sha512 = "a107ba7127f40763325335136c5aeaf6d873dd9ca1c8ca95d93e96b377b41a0974056c84e8323c51ed57e01a2e4ef9996ef2ee2d804053aa2226bd837026523a";
     };
 
     meta = {