Note: For this tweak I recommend using the ChromEdit Plus extension.

With Firefox 2 came the options of changing where your close tab buttons were displayed along with tab-overflow and the List All Tabs buttons. By default the List All Tabs Button is on the right side of the tab bar. You can either move it to the left side of your tab bar or remove the button altogether.

• Moving The Button – To change the location of the List All Tabs button, use the ChromEdit Plus extension. Add these lines to your userChrome.css file located in your profile folder:

   .tabs-alltabs-stack {-moz-box-ordinal-group: 1 !important}
   .tabbrowser-arrowscrollbox {-moz-box-ordinal-group: 2 !important}
   .tabs-closebutton-box {-moz-box-ordinal-group: 3 !important}

  Note: This change will affect the location of the close tab button if the single button at end of bar option is selected on the Close Tab Buttons Tweak.

  Save and restart for Firefox for the changes to take effect.

• Removing The Button – To remove the List All Tabs button, use the ChromEdit Plus extension. Add this line to your userChrome.css file located in your profile folder:Firefox 2

   .tabs-alltabs-stack { display: none !important;}

Firefox 3.6

 .tabs-container > stack  {display:none!important}

When you are done editing your userChrome.css file, close and restart Firefox and the changes should take effect right away.

Firefox 4.0, 5.0, 6.0, 7.0

This button along with the new tab (show below with a yellow border) and tab groups buttons can be removed via the customize… option. Right click on the toolbar and select customize…, then simply grab and drag into the box the buttons you no longer want displayed.

Source: Mozilla Links