diff --git a/mozilla/browser/components/shell/src/nsWindowsShellService.cpp b/mozilla/browser/components/shell/src/nsWindowsShellService.cpp
index bcf4805436c..3f37f6dd558 100644
--- a/mozilla/browser/components/shell/src/nsWindowsShellService.cpp
+++ b/mozilla/browser/components/shell/src/nsWindowsShellService.cpp
@@ -152,6 +152,12 @@ typedef struct {
   PREFIX MID SUFFIX
 
 static SETTING gSettings[] = {
+  // Extension Manager Keys
+  { MAKE_KEY_NAME1(CLS, "MIME\\Database\\Content Type\\application/x-xpinstall;app=firefox"),
+    "Extension",
+    ".xpi",
+    NO_SUBSTITUTION | NON_ESSENTIAL },
+
   // File Extension Aliases
   { MAKE_KEY_NAME1(CLS, ".htm"),    "", CLS_HTML, NO_SUBSTITUTION | NON_ESSENTIAL },
   { MAKE_KEY_NAME1(CLS, ".html"),   "", CLS_HTML, NO_SUBSTITUTION | NON_ESSENTIAL },
diff --git a/mozilla/browser/installer/windows/browser.jst b/mozilla/browser/installer/windows/browser.jst
index cdaae8f3fe7..231491e9d45 100644
--- a/mozilla/browser/installer/windows/browser.jst
+++ b/mozilla/browser/installer/windows/browser.jst
@@ -381,6 +381,11 @@ function updateWinReg()
       winreg.createKey(subkey,"");
       err     = winreg.setValueString(subkey, "", fProgram + "$MainExeFile$");
       err     = winreg.setValueString(subkey, "Path", fProgram);
+
+      // XPInstall content type mappings. 
+      subkey = "SOFTWARE\\Classes\\MIME\\Database\\Content Type\\application/x-xpinstall;app=firefox"
+      winreg.createKey(subkey, "");
+      winreg.setValueString(subkey, "Extension", ".xpi");
     }
 
     winreg.setRootKey(winreg.HKEY_CURRENT_USER);