Disable `ctrl+shift+w` shortcut in Firefox Linux

It is possible to do this with a Firefox add-on. The one I have found in the past is Customizable Shortcuts. You can find it here. It gives you a new page in your Firefox options that allows you to reassign the shortcuts used for each command. For example, I set the close window command that was Ctrl+Shift+W to be something I would never accidentally use, such as Ctrl+Alt+Shift+9. It works pretty well on the Windows version of Firefox, although I admit I don't know about add-on cross compatibility with Linux.

Download and install Autohotkey, create a script called ctrl_shift_w.ahk

#IfWinActive ahk_class MozillaWindowClass

^+w::

return

Load the script by double clicking it.

This will intercept the ctrl+shift+w key sequence.

Autohotkey is very small and installs in just a few seconds.

The confusingly named Menu Wizard Firefox add-on supports customizing keyboard shortcuts. With this add-on you can disable the "Close Window" action associated with Ctrl + Shift + W

The Customizable Shortcuts add-on mentioned in the answer from @techturtle was discontinued by the author in July 2016 and Menu Wizard is a good replacement.

Note : Menu Wizard brings up a one time window after installation asking you to donate and asking if you'd like to install some malware so the author can get paid. Just click No twice and you should be good to go.