Try and check if it helps. http://kb.mozillazine.org/Resizing_oversize_window

%APPDATA%\Mozilla\Firefox\Profiles

Note: I only have experience using one monitor, so apologies if the following doesn't make complete sense for a dual-monitor setup. Sometimes Firefox's 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. You can remove that file and Firefox will return to standard window sizing/positioning. '''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 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? ---- Then, to turn different bars back on, you can use one of these methods to show the toolbar list and select the desired bars there: * right-click a blank spot on the tab bar (or the "+" button) * tap the Alt key to activate the classic menu bar > View > Toolbars * in Customize mode > Show/Hide Toolbars (see: [[Customize Firefox controls, buttons and toolbars]]) To turn on the Menu Bar, Bookmarks Toolbar, or other bars, click it on the list.