TST Lock

This project extends "Tree Style Tab" to help users from accidentally closing a tab via the "X" for tabs that you consider important. Holding "Ctrl + Shift" while clicking on a tab will toggle the "X" with a lock graphic which is non-interactive. (Simply repeat the process to toggle the lock graphic back to the normal "X") You can still close the tab (even with the lock displayed) by right-clicking on the tab and selecting "Close Tab".

Original discussion: https://github.com/piroor/treestyletab/issues/2104

You can change how the lock graphic is sized and positioned by using TST CSS.

In my screenshot example on AMO, I used the following CSS to customize to my liking:

#tabbar tab-item.locked tab-closebox {
  display: initial;
  height: 36px;
  width: 18px; 
  transform: scale(1.3);
  opacity: 1 !important;
}