Under Firefox, while working with multiple tabs, it may happens that you accidentally click on the button to close a particular tab and as result you may lose some important work (such as, the data entered in an online form).
The Close Tab button can be disabled. This implies that to close a particular tab, you will simply have to left click on the tab and scroll to the Close tab option.
In the adress bar of your browser enter: about:config
In the Search bar, enter: browser.tabs.closeButtons
Right click and change the value:
0:Close button is displayed only on active tab.
1:The default value. It shows the close button in all tabs.
2:Completely removes it from all the tabs.
3:Shows a single close button at the end of the tab bar.