If you hover your cursor over the bottom of the page does the taskbar appear?

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Update your Shockwave Flash v14. http://get.adobe.com/shockwave/

Hovering over the bottom of the screen doesn't help.

I just updated it and it doesn't help.

Try this, max and min the window several times.

This article may help;

Firefox Window "off screen" — Remove Settings File

If you can't move or maximize Firefox, you can rename or delete the settings file that stores the last window position.

(1) Open your currently active Firefox settings folder (AKA Firefox profile folder). From the Start menu (Run box or search box), paste this into the search box and press Enter:

%APPDATA%\Mozilla\Firefox\Profiles

This should open a window showing one or more Firefox profile folders. If you have multiple folders, look for the most recent. Click into your profile folder.

(2) If Firefox is still running, right-click it on the Task Bar and Close all Windows.

(3) Wait a few moments for Firefox to finish updating files in your profile folder, then rename localstore.rdf to something else, like localstore-bad.rdf or localstore.old. Alternately, you can delete the file.

(4) You're done with your profile folder and you can restart Firefox now.