Julia, this might help you too.
Basic Troubleshooting
# 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.
# 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).
# In the Firefox Safe Mode dialog, click to put a check mark by Reset all user preferences to Firefox defaults and Reset toolbars and controls.
# To apply your changes, click Make Changes and Restart.