If it's saying that you need to close firefox before you can continue, do this: # Hit Ctrl-Alt-Del # Click Task Manager # After this, you'll want to left click on the process which says "firefox.exe". # You'll also want to close ANYTHING that says "plugin-container.exe", as this is what holds firefox's plug in's and is part of it. If what you've said above is true and it's complaining that you need to close firefox first, then this is all you have to do. Alternatively, if you can't find task manager, simply restart your computer; Firefox doesn't boot on start. You can also make sure that ALL windows are closed from Firefox, including the download window. Any of the above should fix your problem. I also noticed you stated you're using firefox 5.0. The most recent version is 6.0. You can go to http://www.mozilla.com/en-US/firefox/new/ to download the newest version.