If you find yourself accidentally clicking the close button on firefox tabs quite frequently, you can remove that little “x” by following these instructions:

1. In the address bar, type about:config

2. Filter results by typing browser.tabs.closeButtons

3. You will see the current value set at 1.

4. Right click on 1 and choose Modify from the menu.

5. Selecting a value of 3, would remove the close button from individual tabs and put a close button on the right hand corner.

6. Selecting a value of 2 would remove the close button. You will still be able to close the tab by pressing Ctrl+W.