Here you can learn how to change the position of the new tab button for the <ahref="https://addons.mozilla.org/firefox/addon/tree-style-tab/">Tree Style Tab</a> browser extension.
With this change, the new tab button is always at the bottom of the tab tree.
Opening a new tab with the mouse is then as simple as clicking at the bottom left of the screen.
No more aiming at a 20 pixels high region below the last opened tab!
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Simply add the CSS code below to TST's custom style option ("Advanced" > "Extra style rules for contents provided by Tree Style Tab").