diff --git a/toolkit/content/contentAreaUtils.js b/toolkit/content/contentAreaUtils.js
index 024f568def2..8f4eee1b8a7 100644
--- a/toolkit/content/contentAreaUtils.js
+++ b/toolkit/content/contentAreaUtils.js
@@ -490,19 +490,24 @@ function getTargetFile(aData, aSniffer, aContentType, aIsDocument, aSkipPrompt,
     //   mozilla/toolkit/mozapps/downloads/src/nsHelperAppDlg.js.in
     // If you are updating this code, update that code too! We can't share code
     // here since that code is called in a js component.
+    var collisionCount = 0;
     while (file.exists()) {
-      var parts = /.+-(\d+)(\..*)?$/.exec(file.leafName);
-      if (parts) {
-        file.leafName = file.leafName.replace(/((\d+)\.)|((\d+)$)/,
-                                              function (str, dot, dotNum, noDot, noDotNum, pos, s) {
-                                                return (parseInt(str) + 1) + (dot ? "." : "");
-                                              });
+      collisionCount++;
+      if (collisionCount == 1) {
+        // Append "(2)" before the last dot in (or at the end of) the filename
+        // special case .ext.gz etc files so we don't wind up with .tar(2).gz
+        if (file.leafName.match(/\.[^\.]{1,3}\.(gz|bz2|Z)$/i)) {
+          file.leafName = file.leafName.replace(/\.[^\.]{1,3}\.(gz|bz2|Z)$/i, "(2)$&");
+        }
+        else {
+          file.leafName = file.leafName.replace(/(\.[^\.]*)?$/, "(2)$&");
+        }
       }
       else {
-        file.leafName = file.leafName.replace(/\.|$/, "-1$&");
+        // replace the last (n) in the filename with (n+1)
+        file.leafName = file.leafName.replace(/^(.*\()\d+\)/, "$1" + (collisionCount+1) + ")");
       }
     }
-
   }
 
   return file;    
diff --git a/toolkit/mozapps/downloads/src/nsHelperAppDlg.js.in b/toolkit/mozapps/downloads/src/nsHelperAppDlg.js.in
index 6aacde68257..a9560ce23c4 100644
--- a/toolkit/mozapps/downloads/src/nsHelperAppDlg.js.in
+++ b/toolkit/mozapps/downloads/src/nsHelperAppDlg.js.in
@@ -285,16 +285,22 @@ nsUnknownContentTypeDialog.prototype = {
         //   toolkit/content/contentAreaUtils.js.
         // If you are updating this code, update that code too! We can't share code
         // here since this is called in a js component. 
+        var collisionCount = 0;
         while (aLocalFile.exists()) {
-          var parts = /.+-(\d+)(\..*)?$/.exec(aLocalFile.leafName);
-          if (parts) {
-            aLocalFile.leafName = aLocalFile.leafName.replace(/((\d+)\.)|((\d+)$)/,
-                                                              function (str, dot, dotNum, noDot, noDotNum, pos, s) {
-                                                                return (parseInt(str) + 1) + (dot ? "." : "");
-                                                              });
+          collisionCount++;
+          if (collisionCount == 1) {
+            // Append "(2)" before the last dot in (or at the end of) the filename
+            // special case .ext.gz etc files so we don't wind up with .tar(2).gz
+            if (aLocalFile.leafName.match(/\.[^\.]{1,3}\.(gz|bz2|Z)$/i)) {
+              aLocalFile.leafName = aLocalFile.leafName.replace(/\.[^\.]{1,3}\.(gz|bz2|Z)$/i, "(2)$&");
+            }
+            else {
+              aLocalFile.leafName = aLocalFile.leafName.replace(/(\.[^\.]*)?$/, "(2)$&");
+            }
           }
           else {
-            aLocalFile.leafName = aLocalFile.leafName.replace(/\.|$/, "-1$&");
+            // replace the last (n) in the filename with (n+1)
+            aLocalFile.leafName = aLocalFile.leafName.replace(/^(.*\()\d+\)/, "$1" + (collisionCount+1) + ")");
           }
         }
         aLocalFile.create(Components.interfaces.nsIFile.NORMAL_FILE_TYPE, 0600);