Originally Posted by http://texturizer.net/firefox/extensions/

How to install and use an extension
To install an extension from this page, click on the install link. When the installation is complete, restart the browser (all opened windows!). After that, the instructions are different depending on the installed extension. Some extensions add a toolbar button, which requires you to manually add that button by choosing View > Toolbars > Customize... from the menu and then drag-and-drop the button on your toolbar. Other extensions add new settings to the Options window. Select Tools > Options... > Extensions, select the extension and then click Settings to access that window.