Firefox is one of several related browsers that is based on code created by the Mozilla Foundation. Other browsers in this family include Mozilla and Netscape versions 6+. These browsers share a similar foundation, called Gecko, and commonly have a similar interface.
Choose Tools / Options from the menubar. Mac OS X users choose Firefox / Preferences from the menu bar.
Click OK to close the Options/Preferences window.
Screenshot and instructions based on FireFox for Windows. Other versions of Firefox and related browsers may differ from these instructions.