It would be nice to have a clickable button in the toolbar, that toggles the enabled state. It's easy to do (Firefox):
<toolbarbutton
id="httpNowhere-button"
class="httpNowhere-button"
type="menu-button"
label="HTTP Nowhere"
title="HTTP Nowhere"
image="chrome://http-nowhere/skin/httpNowhere-button-enabled.png"
badgeLabel=""
status="disabled"
oncommand="httpNowhere.toggleEnabled();">
...
Thanks