In some instances, changes made to your preferences or configuration may not be remembered by Firefox. This article addresses how to fix the source issue that may result in one or more of the following browser behaviors:

• Changes that you made to your toolbars do not appear when you restart Firefox.
• Changes made to the browser window's size and position are not remembered when you restart Firefox.
• You cannot save bookmarks.

Cause

The above symptoms are caused by a corrupted file, in your Firefox user data, called localstore.rdf. This file is maintained by Firefox to manage some of your local configuration information.

Fixing the problem

1. Close down Firefox completely: At the top of the Firefox window, click the File menu, and select the Exit menu item.Close down Firefox completely: On the menu bar, click the Firefox menu, and select the Quit Firefox menu item.Close down Firefox completely: At the top of the Firefox window, click the File menu, and select the Quit menu item.
2. In Windows, click Start, open the All Programs list, and navigate to the Mozilla Firefox folder. In the Mozilla Firefox folder, select Mozilla Firefox (Safe Mode).Hold down the option key, as you start Firefox.Go to your Terminal and run:

   firefox -safe-mode

   You may need to specify the Firefox installation path (e.g. /usr/lib/firefox-3.5). Firefox should start up with a Firefox Safe Mode dialog.
   
   Note: You can also start Firefox in Safe Mode by clicking Start, selecting Run (or use the Start Search box in Windows 7 and Vista) and then entering the following in the text field:
   

   firefox -safe-mode

3. In the Firefox Safe Mode window, select Reset toolbars and controls.
4. Click Make Changes and Restart.
   
   
   

Based on information from Corrupt localstore.rdf (mozillaZine KB)