If you're missing the search box that normally sits on the right end of the Navigation Toolbar after the URL bar, it might be available to add back in the Customize dialog. To access that you can use either of these:
right-click a blank area of the tab bar > Customize
tap the Alt key > View > Toolbars > Customize
If you find it in the dialog of unused controls, drag it back to the bar.
Occasionally controls will become wrongly sized. In that case, try the "Restore Default Set" button in the Customize dialog to see whether that helps.