firefox-esr-91: init at 91.0esr

(cherry picked from commit d5f7fc95a9ec5798618d10fd04a3ef91aa08de76)

pkgs/applications/networking/browsers/firefox/packages.nix

@@ -30,6 +30,32 @@ rec {
     };
   };
 
+  firefox-esr-91 = common rec {
+    pname = "firefox-esr";
+    ffversion = "91.0esr";
+    src = fetchurl {
+      url = "mirror://mozilla/firefox/releases/${ffversion}/source/firefox-${ffversion}.source.tar.xz";
+      sha512 = "e518e1536094a1da44eb45b3b0f3adc1b5532f17da2dbcc994715419ec4fcec40574fdf633349a8e5de6382942f5706757a35f1b96b11de4754855b9cf7946ae";
+    };
+
+    meta = {
+      description = "A web browser built from Firefox Extended Support Release source tree";
+      homepage = "http://www.mozilla.com/en-US/firefox/";
+      maintainers = with lib.maintainers; [ hexa ];
+      platforms = lib.platforms.unix;
+      badPlatforms = lib.platforms.darwin;
+      broken = stdenv.buildPlatform.is32bit; # since Firefox 60, build on 32-bit platforms fails with "out of memory".
+                                             # not in `badPlatforms` because cross-compilation on 64-bit machine might work.
+      license = lib.licenses.mpl20;
+    };
+    tests = [ nixosTests.firefox-esr-91 ];
+    updateScript = callPackage ./update.nix {
+      attrPath = "firefox-esr-91-unwrapped";
+      versionSuffix = "esr";
+      versionKey = "ffversion";
+    };
+  };
+
   firefox-esr-78 = common rec {
     pname = "firefox-esr";
     ffversion = "78.12.0esr";
@@ -48,7 +74,7 @@ rec {
                                              # not in `badPlatforms` because cross-compilation on 64-bit machine might work.
       license = lib.licenses.mpl20;
     };
-    tests = [ nixosTests.firefox-esr ];
+    tests = [ nixosTests.firefox-esr-78 ];
     updateScript = callPackage ./update.nix {
       attrPath = "firefox-esr-78-unwrapped";
       versionSuffix = "esr";