%APPDATA%\Mozilla\Firefox\Profiles

Sometimes a window gets "off screen" somehow. You often can force it to appear on the screen by right-clicking the little thumbnail image above the Taskbar and choosing Maximize. Does that work? One possible cause for this is that the file which stores window sizes and positions has become corrupted. '''Method #1:''' ''If you can get a maximized window:'' Open your current Firefox settings (AKA Firefox profile) folder using either * "3-bar" menu button > "?" button > Troubleshooting Information * (menu bar) Help > Troubleshooting Information * type or paste about:support in the address bar and press Enter In the first table on the page, click the "Show Folder" button. This should launch a new window listing various files and folders in Windows Explorer. Leaving that window open, switch back to Firefox and Exit, either: * "3-bar" menu button > "power" button * (menu bar) File > Exit Pause while Firefox finishes its cleanup, then rename '''xulstore.json''' to something like xulstore.old. If you see a file named localstore.rdf, rename that one to localstore.old. Start Firefox back up again. Do windows display normally again? '''Method #2:''' ''If you cannot get a Firefox window at all:'' Shut down Firefox by right-clicking the taskbar icon > Close All Windows. Using the Run dialog (windows key + R) or the Start menu search bar (or in Windows 8.x maybe the charms bar search bar?) type or paste the following and press Enter to drill down to the Profiles folder: %APPDATA%\Mozilla\Firefox\Profiles Here you may see one folder -- in which case, double-click into that -- or more than one folder -- in which case, double-click into what looks like the most recently updated. Scroll down and rename '''xulstore.json''' to something like xulstore.old. If you see a file named localstore.rdf, rename that one to localstore.old. Start Firefox back up again. Do windows display normally again?