diff --git a/pkgs/applications/networking/browsers/firefox/common.nix b/pkgs/applications/networking/browsers/firefox/common.nix
index 5dc791631d8b..8060895a2e0f 100644
--- a/pkgs/applications/networking/browsers/firefox/common.nix
+++ b/pkgs/applications/networking/browsers/firefox/common.nix
@@ -138,7 +138,6 @@ stdenv.mkDerivation ({
     "-Wno-error=format-security");
 
   postPatch = ''
-    substituteInPlace third_party/prio/prio/rand.c --replace 'nspr/prinit.h' 'prinit.h'
     rm -rf obj-x86_64-pc-linux-gnu
   '';
 
diff --git a/pkgs/applications/networking/browsers/firefox/packages.nix b/pkgs/applications/networking/browsers/firefox/packages.nix
index 092f4342e158..53924272db16 100644
--- a/pkgs/applications/networking/browsers/firefox/packages.nix
+++ b/pkgs/applications/networking/browsers/firefox/packages.nix
@@ -7,10 +7,10 @@ in
 rec {
   firefox = common rec {
     pname = "firefox";
-    ffversion = "76.0.1";
+    ffversion = "77.0.1";
     src = fetchurl {
       url = "mirror://mozilla/firefox/releases/${ffversion}/source/firefox-${ffversion}.source.tar.xz";
-      sha512 = "0gnhfcgrz6022xf3vqia3s3639xa5pjp13h343d3c09mn8r919cmm6s38vzj1v3734fm25zb68acyarsp72xqq8z1420rh02b2pv38q";
+      sha512 = "ngLihC0YuclLJEV3iPEX+tRzDKIdBe+CCOuFxvWNo7DnX8royOvTj2m4YyWyZoTQ5UCbPTQYmP4otgfovZSe8g==";
     };
 
     patches = [