diff --git a/direct/src/plugin_installer/make_installer.py b/direct/src/plugin_installer/make_installer.py
index 702c3be8cc..9cb1d44475 100755
--- a/direct/src/plugin_installer/make_installer.py
+++ b/direct/src/plugin_installer/make_installer.py
@@ -9,6 +9,11 @@ import zipfile
 from optparse import OptionParser
 import subprocess
 
+try:
+    from hashlib import sha1 as sha
+except ImportError:
+    from sha import sha
+
 usage = """
 This command creates a graphical installer for the
 Panda3D plugin and runtime environment.
@@ -60,8 +65,8 @@ parser.add_option('', '--mssdk', dest = 'mssdk',
                   default = None)
 parser.add_option('-i', '--plugin_root', dest = 'plugin_root',
                   help = 'The root of a directory hierarchy in which the Firefox plugins for various platforms can be found, to build a Firefox xpi file.  This is normally the same as the staging directory populated by the -i parameter to ppackage.  This directory should contain a directory called "plugin", which contains in turn a number of directories named for the platform, by the Panda plugin convention, e.g. linux_i386, osx_ppc, and so on.  Each platform directory should contain a Firefox plugin, e.g. nppanda3d.so.')
-parser.add_option('', '--update_url', dest = 'update_url',
-                  help = "The URL for the Firefox XPI file's updateURL specification.  Optional.")
+parser.add_option('', '--host_url', dest = 'host_url',
+                  help = "The URL at which plugin_root will be hosted.  This is used to construct the update URL for the xpi file.  This is required if you specify --plugin_root.")
 
 (options, args) = parser.parse_args()
 
@@ -101,15 +106,47 @@ install_rdf = """<?xml version="1.0"?>
       <Description>
         <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
         <em:minVersion>3.0</em:minVersion>
-        <em:maxVersion>3.*</em:maxVersion>
+        <em:maxVersion>*</em:maxVersion>
       </Description>
     </em:targetApplication>
     <em:homepageURL>http://www.panda3d.org/</em:homepageURL>
-    %(updateURL)s
+    <em:updateURL>%(host_url)s/plugin/firefox/nppanda3d.rdf</em:updateURL>
   </Description>
 </RDF>
 """
 
+##############################################################################
+#
+# This update.rdf file is used when building a Firefox XPI file.
+#
+##############################################################################
+
+update_rdf = """<?xml version="1.0"?>
+<RDF:RDF xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+         xmlns:em="http://www.mozilla.org/2004/em-rdf#">
+
+  <RDF:Description about="urn:mozilla:item:%(package_id)s">
+    <em:updates>
+      <RDF:Seq>
+        <RDF:li>
+          <RDF:Description>
+            <em:version>%(version)s</em:version>
+            <em:targetApplication>
+              <RDF:Description>
+              <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
+              <em:minVersion>3.0</em:minVersion>
+              <em:maxVersion>*</em:maxVersion>
+              <em:updateLink>%(host_url)s/plugin/firefox/nppanda3d.xpi</em:updateLink>
+              <em:updateHash>sha1:%(xpi_hash)s</em:updateHash>
+            </em:targetApplication>
+          </RDF:Description>
+        </RDF:li>
+      </RDF:Seq>
+    </em:updates>
+  </RDF:Description>
+</RDF:RDF>
+"""
+
 ##############################################################################
 #
 # This Info.plist file is used only for the OSX 10.4 version of packagemaker.
@@ -344,6 +381,10 @@ def makeXpiFile():
     """ Creates a Firefox XPI file, based on the various platform
     version files. """
 
+    if not options.host_url:
+        print "Cannot generate xpi file without --host-url."
+        sys.exit(1)
+
     print "Generating xpi file"
     root = options.plugin_root
     if os.path.isdir(os.path.join(root, 'plugin')):
@@ -353,16 +394,12 @@ def makeXpiFile():
 
     package_id = 'runtime@panda3d.org' #TODO: maybe more customizable?
 
-    updateURL = ''
-    if options.update_url:
-        updateURL = '<em:updateURL>%s</em:updateURL>' % (options.update_url)
-
     tempFile = tempfile.mktemp('.txt', 'p3d_')
     rdf = open(tempFile, 'w')
     rdf.write(install_rdf % {
         'package_id' : package_id,
         'version' : options.version,
-        'updateURL' : updateURL,
+        'host_url' : options.host_url,
         })
     rdf.close()
     xpi.write(tempFile, 'install.rdf')
@@ -386,6 +423,21 @@ def makeXpiFile():
 
             addZipTree(xpi, os.path.join(path, pluginFilename),
                        pluginsXpiDir + '/' + pluginFilename)
+    xpi.close()
+
+    # Now that we've generated the xpi file, get its hash.
+    data = open('nppanda3d.xpi', 'rb').read()
+    xpi_hash = sha(data).hexdigest()
+
+    # And now we can generate the update.rdf file.
+    update = open('update.rdf', 'w')
+    update.write(update_rdf % {
+        'package_id' : package_id,
+        'version' : options.version,
+        'host_url' : options.host_url,
+        'xpi_hash' : xpi_hash,
+        })
+    update.close()
 
 def addZipTree(zip, sourceFile, zipName):
     """ Adds the sourceFile to the zip archive at the indicated name.
diff --git a/direct/src/plugin_standalone/make_osx_bundle.py b/direct/src/plugin_standalone/make_osx_bundle.py
index 720f4be4d3..5f3b9922f6 100755
--- a/direct/src/plugin_standalone/make_osx_bundle.py
+++ b/direct/src/plugin_standalone/make_osx_bundle.py
@@ -44,7 +44,8 @@ def makeBundle(startDir):
     # Generate the bundle directory structure
     rootFilename = Filename(fstartDir)
     bundleFilename = Filename(rootFilename, 'Panda3D.app')
-    shutil.rmtree(bundleFilename.toOsSpecific())
+    if os.path.exists(bundleFilename.toOsSpecific()):
+        shutil.rmtree(bundleFilename.toOsSpecific())
                   
     plistFilename = Filename(bundleFilename, 'Contents/Info.plist')
     plistFilename.makeDir()