Works great! Rated 5 out of 5 stars

I use keyboard shortcuts for openning tabs, so I didn't need that button.

Rated 1 out of 5 stars

Why would u want to remove the New Tab button? Its convenient...

Asked

I was asked to create this add-on by the Mozilla support team because they expect to get support requests to remove this button when Firefox 3.1 comes out.

Rated 5 out of 5 stars

Lol, extension for CSS: .tabs-newtab-button {display:none !important;}
Create extensions to hide all other parts of interface, please. One extension for one part.

Rated 5 out of 5 stars

Removed the button as promised! Everything else still works fine as far as I can tell.