diff --git a/components/greasemonkey.js b/components/greasemonkey.js
index f781deae7..a3e124388 100644
--- a/components/greasemonkey.js
+++ b/components/greasemonkey.js
@@ -10,20 +10,7 @@ var Cu = Components.utils;
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
-var maxJSVersion = (function() {
-  var appInfo = Cc["@mozilla.org/xre/app-info;1"]
-      .getService(Ci.nsIXULAppInfo);
-  var versionChecker = Cc["@mozilla.org/xpcom/version-comparator;1"]
-      .getService(Ci.nsIVersionComparator);
-
-  // Firefox 3.5 and higher supports 1.8.
-  if (versionChecker.compare(appInfo.version, "3.5") >= 0) {
-    return "1.8";
-  }
-
-  // Everything else supports 1.6.
-  return "1.6";
-})();
+var maxJSVersion = "1.6";
 
 var gmSvcFilename = Components.stack.filename;
 var gStartupHasRun = false;
@@ -227,6 +214,11 @@ function startup() {
   loader.loadSubScript("chrome://greasemonkey/content/xmlhttprequester.js");
   loader.loadSubScript("chrome://greasemonkey/content/scriptdownloader.js");
   loader.loadSubScript("chrome://greasemonkey/content/third-party/mpl-utils.js");
+
+  // Firefox 3.5 and higher supports 1.8.
+  if (GM_compareFirefoxVersion("3.5") >= 0) {
+    return "1.8";
+  }
 }
 
 /////////////////////////////////// Service ////////////////////////////////////
diff --git a/content/addons.js b/content/addons.js
index 35ae53276..77f63795a 100644
--- a/content/addons.js
+++ b/content/addons.js
@@ -6,20 +6,14 @@ var gUserscriptsView = null;
 var GM_firefoxVersion;
 var GM_os;
 (function() {
-var appInfo = Components
-    .classes["@mozilla.org/xre/app-info;1"]
-    .getService(Components.interfaces.nsIXULAppInfo);
-var versionChecker = Components
-    .classes["@mozilla.org/xpcom/version-comparator;1"]
-    .getService(Components.interfaces.nsIVersionComparator);
 var xulRuntime = Components
     .classes["@mozilla.org/xre/app-info;1"]
     .getService(Components.interfaces.nsIXULRuntime);
 
 // Detect fixed possible compatible Firefox versions.
-if (versionChecker.compare(appInfo.version, '3.5') < 0) {
+if (GM_compareFirefoxVersion('3.5') < 0) {
   GM_firefoxVersion = '3.0';
-} else if (versionChecker.compare(appInfo.version, '3.6') < 0) {
+} else  if (GM_compareFirefoxVersion('3.6') < 0) {
   GM_firefoxVersion = '3.5';
 } else {
   GM_firefoxVersion = '3.6';
diff --git a/content/browser.js b/content/browser.js
index a41612503..ae73d2ad2 100644
--- a/content/browser.js
+++ b/content/browser.js
@@ -66,11 +66,7 @@ GM_BrowserUI.chromeLoad = function(e) {
   // what we want, instead we listen for dom-window-destroyed, which comes
   // pretty close (at least it doesn't leak memory).  But: listening for dom-
   // in Firefox 4 causes breakage, so we just do either-or.
-  var appInfo = Cc["@mozilla.org/xre/app-info;1"]
-      .getService(Ci.nsIXULAppInfo);
-  var versionChecker = Cc["@mozilla.org/xpcom/version-comparator;1"]
-      .getService(Ci.nsIVersionComparator);
-  if (versionChecker.compare(appInfo.version, "4.0") >= 0) {
+  if (GM_compareFirefoxVersion("4.0") >= 0) {
     observerService.addObserver(GM_BrowserUI, "inner-window-destroyed", true);
   } else {
     observerService.addObserver(GM_BrowserUI, "dom-window-destroyed", true);
diff --git a/content/utils.js b/content/utils.js
index 971c9e14a..ce687668d 100644
--- a/content/utils.js
+++ b/content/utils.js
@@ -283,6 +283,16 @@ function GM_compareVersions(aV1, aV2) {
   return 0;
 }
 
+/** Runs nsIVersionComparator.compare() on the Firefox version. */
+function GM_compareFirefoxVersion(aTarget) {
+  var appInfo = Cc["@mozilla.org/xre/app-info;1"]
+      .getService(Ci.nsIXULAppInfo);
+  var versionChecker = Cc["@mozilla.org/xpcom/version-comparator;1"]
+      .getService(Ci.nsIVersionComparator);
+
+  return versionChecker.compare(appInfo.version, aTarget);
+}
+
 // Remove all children from an element.
 function GM_emptyEl(el) {
   while (el.firstChild) el.removeChild(el.firstChild);