Workaround Bug 489729 - Clicking a tab once and then moving your mouse in a downward motion causes a new window to open.
Fixed with builds on Minefield3.6a2pre on 2009-08-10 and Shiretoko3.5.4pre on 2009-08-25.
However, it seems to be STILL TOO SENSITIVE. In such a case it is effective to install this extension.
Just to install this.
[OPTION](If you want)
1. Disabled the detaching of the tab completely.
2. Enable to create Shortcut on the desctop/explorer.
When enable drop of the URL with an option, depending on application, detaching tab and drop of URL are carried out at the same time.
If you want to undo detach and tear off tab, try "Undo Detach Tab" extension (https://addons.mozilla.org/en-US/firefox/addon/12689/