overlay chrome://browser/content/browser.xul chrome://sample/content/browser.xul
style chrome://global/content/customizeToolbar.xul chrome://sample/skin/button.css
<?xml version="1.0"?>
<?xml-stylesheet href="chrome://sample/skin/button.css" type="text/css"?>
<overlay id="sampleOverlay"
xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
<toolbarpalette id="BrowserToolbarPalette">
<toolbarbutton id="restartButton"
label="再起動"
tooltiptext="Firefox を再起動します"
class="toolbarbutton-1 chromeclass-toolbar-additional"
oncommand="Application.restart();"/>
</toolbarpalette>
</overlay>
#restartButton {
list-style-image : url("chrome://sample/skin/restart.png");
}