So whats a sidebar? Its just displays and application/addon in a column next to the web pages being viewed. Delicious and Facebook are example of addon that uses Sidebars.
Disable the sidebarStep 1. Disable sidebar
At the top of the sidebar, click on the gear.
Uncheck the "Show sidebar".
Step 1. Add Sidebar item to the Firefox menu.
Click on the Firefox menu, choose "Customize"
Step 2. Turn on Sidebar.
Click on Firefox menu, choose Sidebars.
Click on the Application available for Sidebars. In this case its the Delicious bookmarks.