Try to delete localstore.rdf:

• http://kb.mozillazine.org/Corrupt_localstore.rdf

You can try to open the system menu of that Firefox window via Alt+Space and see if you can move and resize that window.
If that works then close Firefox (File > Exit/Quit) to save that setting.

I tried both of those suggestions and neither one worked.

Were you able to open the system menu via Alt+Space in the hidden Firefox window?

You will first have to move the not maximized window into view and then resize it if necessary.

• Use Restore or Maximize in the right-click context menu of the Taskbar icon to set focus to the Firefox application if you do not see the Firefox window.
• Open the system menu of that Firefox window via Alt+Space and see if you can move and resize that window.

If that works then close Firefox (File > Exit/Quit) to save that setting.

In the old days, Firefox would allow certain script commands to reposition an existing window, but that has been restricted to prevent mischievous sites from hiding their windows off-screen. But it also makes this kind of situation difficult to recover from.

If the off-screen window just has one tab, such as your home page, you could try the following.

(1) Copy the following line of code to the clipboard:

newwin=window.open(window.location.href);newwin.moveTo(0,0);

(2) Make the offscreen window active, then press Ctrl+Shift+k to open the web console. (Obviously you can't see it, but unless the cursor is in a plugin the page, this should work.)

(3) Press Ctrl+v to paste the line of code then press Enter to run it. A new copy of that page should open in a window positioned at the top left of the screen.

(4) Make the off-screen window active again and press Ctrl+w to close it.

Firefox should remember the location of the last window you close, so hopefully this will resolve the issue going forward.

Any luck?

Edit: Simplified procedure, since you can maximize the window (duh!):

(1) Copy the following line of code to the clipboard:

newwin=window.open(window.location.href);newwin.moveTo(0,0);

(2) In the maximized window, press Ctrl+Shift+k to open the web console.

(3) Press Ctrl+v to paste the line of code then press Enter to run it. A new copy of that page should open in a window positioned at the top left of the screen.

(4) Switch back to the maximized window and close it.

jscher2000 your method worked, thanks so much!!

I don't know much about computers, but I followed your instructions and the problem is fixed. Thank you so much. Randy