--- a/browser/modules/WebappsInstaller.jsm
+++ b/browser/modules/WebappsInstaller.jsm
@@ -462,18 +462,19 @@ MacNativeApp.prototype = {
     //  host of the app origin + ";" +
     //  protocol + ";" +
     //  port (-1 for default port)
     this.appProfileDir = this.appSupportDir.clone();
     this.appProfileDir.append(this.launchURI.host + ";" +
                               this.launchURI.scheme + ";" +
                               this.launchURI.port);
 
-    this.installDir = Services.dirsvc.get("LocApp", Ci.nsILocalFile);
+    this.installDir = Services.dirsvc.get("TmpD", Ci.nsILocalFile);
     this.installDir.append(this.appNameAsFilename + ".app");
+    this.installDir.createUnique(Ci.nsIFile.DIRECTORY_TYPE, 0755);
 
     this.contentsDir = this.installDir.clone();
     this.contentsDir.append("Contents");
 
     this.macOSDir = this.contentsDir.clone();
     this.macOSDir.append("MacOS");
 
     this.resourcesDir = this.contentsDir.clone();
@@ -491,17 +492,17 @@ MacNativeApp.prototype = {
       this._createDirectoryStructure();
       this._copyPrebuiltFiles();
       this._createConfigFiles();
     } catch (ex) {
       this._removeInstallation(false);
       throw(ex);
     }
 
-    getIconForApp(this, this._createPListFile);
+    getIconForApp(this, this._moveToApplicationsFolder);
   },
 
   _removeInstallation: function(keepProfile) {
     try {
       if(this.installDir.exists()) {
         this.installDir.followLinks = false;
         this.installDir.remove(true);
       }
@@ -519,17 +520,16 @@ MacNativeApp.prototype = {
     } catch(ex) {
     }
   },
 
   _createDirectoryStructure: function() {
     if (!this.appProfileDir.exists())
       this.appProfileDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0755);
 
-    this.installDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0755);
     this.contentsDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0755);
     this.macOSDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0755);
     this.resourcesDir.create(Ci.nsIFile.DIRECTORY_TYPE, 0755);
   },
 
   _copyPrebuiltFiles: function() {
     let webapprt = this.processFolder.clone();
     webapprt.append("webapprt-stub");
@@ -557,19 +557,17 @@ MacNativeApp.prototype = {
 
     let factory = Cc["@mozilla.org/xpcom/ini-processor-factory;1"]
                     .getService(Ci.nsIINIParserFactory);
 
     let writer = factory.createINIParser(applicationINI).QueryInterface(Ci.nsIINIParserWriter);
     writer.setString("Webapp", "Name", this.appName);
     writer.setString("Webapp", "Profile", this.appProfileDir.leafName);
     writer.writeFile();
-  },
 
-  _createPListFile: function() {
     // ${InstallDir}/Contents/Info.plist
     let infoPListContent = '<?xml version="1.0" encoding="UTF-8"?>\n\
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">\n\
 <plist version="1.0">\n\
   <dict>\n\
     <key>CFBundleDevelopmentRegion</key>\n\
     <string>English</string>\n\
     <key>CFBundleDisplayName</key>\n\
@@ -597,16 +595,27 @@ MacNativeApp.prototype = {
   </dict>\n\
 </plist>';
 
     let infoPListFile = this.contentsDir.clone();
     infoPListFile.append("Info.plist");
     writeToFile(infoPListFile, infoPListContent, function() {});
   },
 
+  _moveToApplicationsFolder: function() {
+    let appDir = Services.dirsvc.get("LocApp", Ci.nsILocalFile);
+    let destination = getAvailableFile(appDir,
+                                       this.appNameAsFilename,
+                                       ".app");
+    if (!destination) {
+      return false;
+    }
+    this.installDir.moveTo(destination.parent, destination.leafName);
+  },
+
   /**
    * 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.
    */
   useTmpForIcon: true,
 
@@ -681,16 +690,57 @@ function stripStringForFilename(aPossibl
   let stripFrontRE = new RegExp("^\\W*","gi");
   let stripBackRE = new RegExp("\\W*$","gi");
 
   let stripped = aPossiblyBadFilenameString.replace(stripFrontRE, "");
   stripped = stripped.replace(stripBackRE, "");
   return stripped;
 }
 
+/**
+ * Finds a unique name available in a folder (i.e., non-existent file)
+ *
+ * @param aFolder nsIFile that represents the directory where we want to write
+ * @param aName   string with the filename (minus the extension) desired
+ * @param aExtension string with the file extension, including the dot
+
+ * @return nsILocalFile or null if folder is unwritable or unique name
+ *         was not available
+ */
+function getAvailableFile(aFolder, aName, aExtension) {
+  let folder = aFolder.QueryInterface(Ci.nsILocalFile);
+  folder.followLinks = false;
+  if (!folder.isDirectory() || !folder.isWritable()) {
+    return null;
+  }
+
+  let file = folder.clone();
+  file.append(aName + aExtension);
+
+  if (!file.exists()) {
+    return file;
+  }
+
+  for (let i = 2; i < 10; i++) {
+    file.leafName = aName + " (" + i + ")" + aExtension;
+    if (!file.exists()) {
+      return file;
+    }
+  }
+
+  for (let i = 10; i < 100; i++) {
+    file.leafName = aName + "-" + i + aExtension;
+    if (!file.exists()) {
+      return file;
+    }
+  }
+
+  return null;
+}
+
 function escapeXML(aStr) {
   return aStr.toString()
              .replace(/&/g, "&amp;")
              .replace(/"/g, "&quot;")
              .replace(/'/g, "&apos;")
              .replace(/</g, "&lt;")
              .replace(/>/g, "&gt;");
 }