home: firefox: add ff2mpv

This allows watching videos using mpv via a simple button.

home/firefox/default.nix

@@ -11,6 +11,15 @@
         default = config.my.home.firefox.enable;
       };
     };
+
+    ff2mpv = {
+      enable = mkOption {
+        type = types.bool;
+        description = "ff2mpv configuration";
+        example = false;
+        default = config.my.home.mpv.enable;
+      };
+    };
   };
 
   imports = [