You can try to clear the Windows icon cache.

Open the Task Manager (Shift+Ctrl+ESC) In the Process tab, right-click on the Explorer.exe process and select End Process.

Open the file picker via "File > New Task (Run)" and click the Browse button. Type or Paste %userprofile%\AppData\Local in the File name field (AppData is a hidden folder).

Select the file IconCache.db and use Delete in the right-click context menu to delete the file.

After the IconCache.db has been deleted, start a new explorer.exe process via "File > New Task" to get the desktop and Taskbar back.

I'm having the same issue (icon changed to a pad with pencil, ruler and brush after updating to 10.0.2) but on Apple OS 10 Lion.

Try the solution from this thread for the pencil icon on Mac:

• [/questions/883573]

• Delete the Firefox icon from the dock.
• Create a new icon by dragging the Firefox application to the dock.

THE EASY WAY...... to get back the default Firefox icon back to your taskbar in Window 7:

1 Click on the 'Start Button' on your task bar, then 'All Programs' and find 'Mozilla Firefox' (If you see the 'Firefox' icon here then jump to step 7)

2 Right click on 'Mozilla Firefox' and select 'Properties'

3 Under the 'Shortcut' tab, near the bottom, click on the 'Change Icon...' button

4 Select the icon you prefer then click 'OK' which brings you back to the 'Mozilla Firefox Properties' screen

5 Click on the 'Apply' button at the bottom of this window then 'OK' to close the 'Mozilla Firefox Properties' window

6 Go back to 'Start' then 'All Programs' and locate 'Mozilla Firefox' which should now have the desired icon beside it

7 Right click on 'Mozilla Firefox' and from the menu select 'Pin to Task Bar'

8 Finally, remove the undesired icon from the task bar by right clicking on it and selecting 'Unpin this program from taskbar'.