If you're missing your menu bar, press ALT or F10 in your keyboard to make the Menu Bar temporarily visible. If you want it to be permanently visible, go into View > Toolbars > Menu Bar, or right-click the Navigation Toolbar (the Reload button, for example) and select Menu Bar.
If this doesn't help, right-click the navigation toolbar, select Customize... and click Restore Default Set. If it doesn't appear right away, try pressing ALT or F10. You can go into View > Toolbars > Menu Bar to make it permanently visible, or right-click the Navigation Toolbar and select Menu Bar.
If none of this helps, you may be having a problem with some Firefox add-on that is hindering your Firefox's normal behavior. Try disabling all add-ons (just to check), to see if Firefox goes back to normal.