--- a/toolkit/mozapps/extensions/content/extensions-content.js
+++ b/toolkit/mozapps/extensions/content/extensions-content.js
@@ -230,25 +230,16 @@ function InstallTriggerManager() {
     self.callbacks = null;
   }, false);
 }
 
 InstallTriggerManager.prototype = {
   handleEvent: function handleEvent(aEvent) {
     var window = aEvent.target.defaultView;
 
-    // Need to make sure we are called on what we care about -
-    // content windows. DOMWindowCreated is called on *all* HTMLDocuments,
-    // some of which belong to chrome windows or other special content.
-    //
-    var uri = window.document.documentURIObject;
-    if (uri.scheme === "chrome" || uri.spec.split(":")[0] == "about") {
-      return;
-    }
-
     window.wrappedJSObject.__defineGetter__("InstallTrigger", function() {
       // We do this in a getter, so that we create these objects
       // only on demand (this is a potential concern, since
       // otherwise we might add one per iframe, and keep them
       // alive for as long as the tab is alive).
 
       delete window.wrappedJSObject.InstallTrigger;
       var installTrigger = createInstallTrigger(window.wrappedJSObject);

--- a/toolkit/mozapps/extensions/test/xpinstall/Makefile.in
+++ b/toolkit/mozapps/extensions/test/xpinstall/Makefile.in
@@ -91,16 +91,17 @@ include $(topsrcdir)/config/rules.mk
                  browser_httphash2.js \
                  browser_httphash3.js \
                  browser_httphash4.js \
                  browser_httphash5.js \
                  browser_httphash6.js \
                  browser_badargs.js \
                  browser_badargs2.js \
                  browser_bug611242.js \
+                 browser_bug638292.js \
                  unsigned.xpi \
                  signed.xpi \
                  signed2.xpi \
                  signed-no-o.xpi \
                  signed-no-cn.xpi \
                  signed-untrusted.xpi \
                  signed-tampered.xpi \
                  theme.xpi \
@@ -114,13 +115,14 @@ include $(topsrcdir)/config/rules.mk
                  installtrigger_frame.html \
                  startsoftwareupdate.html \
                  installchrome.html \
                  triggerredirect.html \
                  authRedirect.sjs \
                  cookieRedirect.sjs \
                  hashRedirect.sjs \
                  bug540558.html \
+                 bug638292.html \
                  redirect.sjs \
                  $(NULL)
 
 libs::	$(_BROWSER_FILES)
 	$(INSTALL) $(foreach f,$^,"$f") $(DEPTH)/_tests/testing/mochitest/browser/$(relativesrcdir)

new file mode 100644
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/xpinstall/browser_bug638292.js
@@ -0,0 +1,53 @@
+// ----------------------------------------------------------------------------
+// Test whether an InstallTrigger.enabled is working
+function test() {
+  waitForExplicitFinish();
+
+  gBrowser.selectedTab = gBrowser.addTab();
+  gBrowser.selectedBrowser.addEventListener("load", function() {
+    gBrowser.selectedBrowser.removeEventListener("load", arguments.callee, true);
+    waitForFocus(page_loaded, gBrowser.contentWindow);
+  }, true);
+  gBrowser.loadURI(TESTROOT + "bug638292.html");
+}
+
+function check_load(aCallback) {
+  gBrowser.addEventListener("load", function(aEvent) {
+    gBrowser.removeEventListener("load", arguments.callee, true);
+
+    // Let the load handler complete
+    executeSoon(function() {
+      var doc = gBrowser.browsers[2].contentDocument;
+      is(doc.getElementById("enabled").textContent, "true", "installTrigger should have been enabled");
+
+      // Focus the old tab
+      gBrowser.selectedTab = gBrowser.tabs[1];
+      waitForFocus(function() {
+        // Close the new tab
+        gBrowser.removeTab(gBrowser.tabs[2]);
+        aCallback();
+      }, gBrowser.contentWindow);
+    });
+  }, true);
+}
+
+function page_loaded() {
+  var doc = gBrowser.contentDocument;
+  info("Clicking link 1");
+  EventUtils.synthesizeMouseAtCenter(doc.getElementById("link1"), { }, gBrowser.contentWindow);
+
+  check_load(function() {
+    info("Clicking link 2");
+    EventUtils.synthesizeMouseAtCenter(doc.getElementById("link2"), { }, gBrowser.contentWindow);
+
+    check_load(function() {
+      info("Clicking link 3");
+      EventUtils.synthesizeMouseAtCenter(doc.getElementById("link3"), { button: 1 }, gBrowser.contentWindow);
+
+      check_load(function() {
+        gBrowser.removeCurrentTab();
+        finish();
+      });
+    });
+  });
+}

new file mode 100644
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/xpinstall/bug638292.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+<html>
+
+<!-- This page tests InstallTrigger is defined in a new window -->
+
+<head>
+<title>InstallTrigger tests</title>
+</head>
+<body>
+<p>InstallTrigger tests</p>
+<p><a id="link1" target="_blank" href="enabled.html">Open window with target</a></p>
+<p><a id="link2" onclick="window.open(this.href); return false" href="enabled.html">Open window with JS</a></p>
+<p><a id="link3" href="enabled.html">Open window with middle-click</a></p>
+</body>
+</html>