Possibly something has gone wrong, or you may just have inadvertently changed the settings.

In most systems there is a Firefox button instead of a long menu toolbar.

• Display the Firefox button menu instead of the menu toolbar

You will also have options to display your bookmarks and navigation toolbars.

• Customize Firefox controls, buttons and toolbars

Try to remove the Firefox plist file (org.mozilla.firefox.plist).

• http://www.macfixit.com/article.php?story=20060606082246983 How .plist files become corrupt and troubleshooting the results

Go to "~/Library/Preferences" and remove the plist file for Firefox (org.mozilla.firefox.plist)

Try to repair the disk permissions:

• http://thexlab.com/faqs/repairprocess.html

You can check for problems with the localstore.rdf file.

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

On Mac you can use command+Shift+F to toggle full screen mode.

• https://support.mozilla.org/kb/how-to-use-full-screen