If you right-click somewhere does "Take Screenshot" show in the menu? If so, then try right-clicking somewhere on the toolbar and select "Customize Toolbar". You should see a screenshot button there somewhere that you can drag onto the toolbar. If not, then perhaps the extension was disabled in <code>about:config</code>. Check <code>about:config</code> and make sure <code>extensions.screenshots.disabled</code> is set to <b><code>false</code></b>. If it was set to <code>true</code> then you'll need to restart the browser first. Then, you can customize the toolbar to add the button back.