Make sure the downloads is also closed. Then make sure the program is turned off by opening the task manager, you can do that by pressing ctrl+alt+del together, then select task manager if it doesn't open automatically.
In task manager, open the processed tab, Look for firefox, select it and click end process or program. or just press the delete button and it closes it.
ones all firefoxes are closed try again with your program.
Answers & Comments
Make sure the downloads is also closed. Then make sure the program is turned off by opening the task manager, you can do that by pressing ctrl+alt+del together, then select task manager if it doesn't open automatically.
In task manager, open the processed tab, Look for firefox, select it and click end process or program. or just press the delete button and it closes it.
ones all firefoxes are closed try again with your program.
Go to add remover program in the control panel and remove firefox from the computer. Download a new copy and reinstall it from the link below.
http://www.mozilla.com/en-US/firefox/ie.html
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Smith