The "PermaTabs Mod" extension for Firefox can help keep important tabs to services such as Twitter and Gmail from accidentally being closed.
While browsing the web in Mozilla Firefox, do you often keep tabs open for sites and services such as Twitter and Gmail? If so, you may find it irritating when you accidentally close these tabs by clicking the wrong "X" button, clicking the "Close Other Tabs" menu item, etc.
With the "Permatabs Mod" add-on you can designate certain tabs as permanent so they should never close. These tabs will be marked in a different color, will not display an "X", and even the context menu will be modified so that right-clicking such a tab will show "Close tab" grayed out....
Read more at MalekTips.