"F11" toggles Full Screen mode on/off see * Firefox and other Browser Keyboard Shortcuts (Comparison Table)<br>http://www.mvps.org/dmcritchie/firefox/keyboard.htm Not to be confused with Maximize/Restore button in upper right corner which leaves your toolbars intact. Just noticed your mention of missing the red "X" (red background), are you also missing the vertical scrollbar on the right side. * Resizing oversize window - MozillaZine Knowledge Base<br>http://kb.mozillazine.org/Resizing_oversize_window If you are referring to not being able to close a tab, you will not see the "X" on a tab if it is the last tab, in fact you may not even see the tab bar, that depends on your options and on configuration options for how the close tab is to appear. Check your '''[http://kb.mozillazine.org/About:config_entries about:config]''' options :The following options are found within these two articles * About:config entries - MozillaZine Knowledge Base<br>http://kb.mozillazine.org/About:config_entries * Tabs configuration, extracted from About:config entries - MozillaZine Knowledge Base<br>http://dmcritchie.mvps.org/firefox/tabs_config.htm '''browser.abs.autoHide''' Boolean :Behavior for the tab bar when only one tab exists :True (default): Hide the tab bar :False: Always show the tab bar :Note: In Firefox, this can be changed via "Tools → Options → Tabs → Always show the tab bar (Firefox 2 and above) or Tools → Options → Tabs → Hide the tab bar when only one web site is open (Firefox 1.5). '''browser.tabs.closeButtons''' Integer (Firefox 2.0) :This preference controls how close buttons can be displayed on tabs. :0: Display a close button on the active tab only :1: (default) Display a close button on each tab :2: Don't display any close buttons :3: Display a single close button at the end of the tab bar (Firefox 1.x behavior) <br><small>Please mark "Solved" one answer that will best help others with a similar problem -- hope this was it. But please also leave a comment because of the several possibilities and we would like to know which problem you actually experienced. </small>