diff --git a/modules/programs/firefox/mkFirefoxModule.nix b/modules/programs/firefox/mkFirefoxModule.nix
index 8007a9a49..33c022890 100644
--- a/modules/programs/firefox/mkFirefoxModule.nix
+++ b/modules/programs/firefox/mkFirefoxModule.nix
@@ -24,6 +24,7 @@ let
     mkIf
     mkMerge
     mkOption
+    mkOptionDefault
     optionalString
     optional
     setAttrByPath
@@ -235,6 +236,12 @@ in
       '';
     };
 
+    release = mkOption {
+      internal = true;
+      type = types.str;
+      description = "Upstream release version used to fetch from `releases.mozilla.org`.";
+    };
+
     languagePacks = mkOption {
       type = types.listOf types.str;
       default = [ ];
@@ -242,7 +249,9 @@ in
         The language packs to install. Available language codes can be found
         on the releases page:
         `https://releases.mozilla.org/pub/firefox/releases/''${version}/linux-x86_64/xpi/`,
-        replacing `''${version}` with the version of ${appName} you have.
+        replacing `''${version}` with the version of ${appName} you have. If
+        the version string of your Firefox derivative diverts from the upstream
+        version, try setting the `release` option.
       '';
       example = [
         "en-GB"
@@ -952,6 +961,7 @@ in
     }
     // setAttrByPath modulePath {
       finalPackage = wrapPackage cfg.package;
+      release = mkOptionDefault (builtins.head (lib.splitString "-" cfg.package.version));
 
       policies = {
         ExtensionSettings = lib.mkIf (cfg.languagePacks != [ ]) (
@@ -960,7 +970,7 @@ in
               lang:
               lib.nameValuePair "langpack-${lang}@firefox.mozilla.org" {
                 installation_mode = "normal_installed";
-                install_url = "https://releases.mozilla.org/pub/firefox/releases/${cfg.package.version}/linux-x86_64/xpi/${lang}.xpi";
+                install_url = "https://releases.mozilla.org/pub/firefox/releases/${cfg.release}/linux-x86_64/xpi/${lang}.xpi";
               }
             ) cfg.languagePacks
           )