ATTENTION: as ssokolow stated, it changes toolbars, like you're on HTML tab, then after some seconds it changes to inline code finder one! second bug: even if you disable firebug and inline code finder, you still see the lines red-green you see in screenshoot. Wait for an update.
Firebug is nothing short of amazing, so I like it when other authors can extend its functionality with ideas such as this one. Works a lot better when it's part of Firebug than its stand-alone extension counterpart, as it allows me to stick to my current work flow.