--- a/toolkit/webapps/WebappsInstaller.jsm
+++ b/toolkit/webapps/WebappsInstaller.jsm
@@ -105,18 +105,16 @@ function NativeApp(aData) {
     shortDesc = firstLine.length <= 256
                 ? firstLine
                 : firstLine.substr(0, 253) + "...";
   }
   this.shortDescription = sanitize(shortDesc);
 
   this.appcacheDefined = (app.manifest.appcache_path != undefined);
 
-  this.manifest = app.manifest;
-
   // The app registry is the Firefox profile from which the app
   // was installed.
   this.registryFolder = Services.dirsvc.get("ProfD", Ci.nsIFile);
 
   this.webappJson = {
     "registryDir": this.registryFolder.path,
     "app": app
   };
@@ -761,16 +759,51 @@ LinuxNativeApp.prototype = {
                     .getService(Ci.nsIToolkitProfileService);
 
     try {
       this.appProfile = profSvc.createDefaultProfileForApp(this.installDir.leafName,
                                                            null, null);
     } catch (ex if ex.result == Cr.NS_ERROR_ALREADY_INITIALIZED) {}
   },
 
+  /**
+   * Translate marketplace categories to freedesktop.org categories.
+   *
+   * @link http://standards.freedesktop.org/menu-spec/menu-spec-latest.html#category-registry
+   *
+   * @return an array of categories
+   */
+  _translateCategories: function() {
+    let translations = {
+      "books-reference": "Education;Literature",
+      "business": "Finance",
+      "education": "Education",
+      "entertainment-sports": "Amusement;Sports",
+      "games": "Game",
+      "health-fitness": "MedicalSoftware",
+      "lifestyle": "Amusement",
+      "music": "Audio;Music",
+      "news-weather": "News",
+      "photos-media": "AudioVideo",
+      "productivity": "Office",
+      "shopping": "Amusement",
+      "social": "Chat",
+      "travel": "Amusement",
+      "utilities": "Utility"
+    };
+
+    // The trailing semicolon is needed as written in the freedesktop specification
+    let categories = "";
+    for (let category of this.app.categories) {
+      categories += translations[category] + ";";
+    }
+
+    return categories;
+  },
+
   _createConfigFiles: function() {
     // ${InstallDir}/webapp.json
     writeToFile(this.configJson, JSON.stringify(this.webappJson), function() {});
 
     let factory = Cc["@mozilla.org/xpcom/ini-processor-factory;1"]
                     .getService(Ci.nsIINIParserFactory);
 
     // ${InstallDir}/webapp.ini
@@ -785,16 +818,21 @@ LinuxNativeApp.prototype = {
 
     writer = factory.createINIParser(this.desktopINI).QueryInterface(Ci.nsIINIParserWriter);
     writer.setString("Desktop Entry", "Name", this.appName);
     writer.setString("Desktop Entry", "Comment", this.shortDescription);
     writer.setString("Desktop Entry", "Exec", '"'+this.webapprt.path+'"');
     writer.setString("Desktop Entry", "Icon", this.iconFile.path);
     writer.setString("Desktop Entry", "Type", "Application");
     writer.setString("Desktop Entry", "Terminal", "false");
+
+    let categories = this._translateCategories();
+    if (categories)
+      writer.setString("Desktop Entry", "Categories", categories);
+
     writer.writeFile();
   },
 
   /**
    * This variable specifies if the icon retrieval process should
    * use a temporary file in the system or a binary stream. This
    * is accessed by a common function in WebappsIconHelpers.js and
    * is different for each platform.