http://www.heerengandhi.com/2009/07/29/firefox-icon-went-missing-in-windows-7-heres-a-fix/comment-page-1/
- Close all folder windows that are currently open.
- Launch Task Manager using the CTRL+SHIFT+ESC key sequence, or by running taskmgr.exe
- In the Process tab, right-click on the Explorer.exe process and select End Process
- Click the End process button when asked for confirmation.
- From the File menu of Task Manager, select New Task (Run…)
- Type CMD.EXE, and click OK
- In the Command Prompt window, type the commands one by one and press ENTER after each command:
CD /d %userprofile%\AppData\Local
DEL IconCache.db /a
EXIT
- In Task Manager, click File, select New Task (Run…)
- Type EXPLORER.EXE, and click OK.